Epidemiology Ucc

Question 1

State two measures of disease frequency

Answer 1

Prevalence and incidence rates
Case fatality ratio

Question 2

The word epidemiology comes from the Greek words epi,demos and logos. What do these three words mean?

the word epidemiology has its roots in the study of what?

Answer 2

The word epidemiology comes from the Greek words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of.
• In other words, the word epidemiology has its roots in the study of what befalls a population

Question 3

What is epidemiology

Answer 3

Epidemiology is the (study) of the (distribution) and (determinants) of (health-related states or events) in (specified populations), and the (application of this study to the prevention and control of health problems).
The above definition is for “Epidemiology as a discipline”

Question 4

State the two types of epidemiology

Answer 4

Descriptive and analytical epidemiology

Question 5

What is distribution in terms of epidemiology
What is frequency
What is the use of frequency?
What is a pattern?

Answer 5

Distribution:
In Epidemiology,it is concerned with the frequency and pattern of health events in a population
•Frequency refers to the number of health events e.g. the number of cases of meningitis or diabetes in a population, and also to the relationship of that number to the size of the population.
•This allows epidemiologists to compare disease occurrence across different populations.
•Pattern refers to the occurrence of health-related events by time, place, and person.

Characterizing health events by time, place, and person are activities of descriptive epidemiology

Question 6

What is descriptive epidemiology

Answer 6

Descriptive epidemiology: It describes the disease occurrence and other health-related characteristics among human populations in terms of person (“who”: age, sex, ethnicity, religion), place (“where”: districts, country, municipality) and time (“when”: year, season, day,minutes,hours )

Example is conditions that affect children, those that affect women,those that affect men .this is all by descriptive epidemiology

Example: The percentage of malaria cases among pregnant women in Kintampo South District in 2005 was 35%

Question 7

What is a determinant?
What do epidemiologists do to search for determinants of events.

Answer 7

Epidemiology is also used to search for determinants. Determinants are the causes and other factors that influence the occurrence of disease and other health-related events.
• Epidemiologists assume that illness does not occur randomly in a population, but happens only when the right accumulation of risk factors or determinants exists in an individual.
-To search for these determinants, epidemiologists use analytic epidemiology or epidemiologie studies to provide the “Why” and “How” of such

Example is predisposing factors that lead to someone getting stroke. So the risk factors are the determinants

Question 8

What is analytical epidemiology

Answer 8

Analytical epidemiology: This examines the association or relationship between a given health status or events and possible causative or protective factors

Example: health event is the diarrhea and the causative or protective factors is the breastfeeding. So questions for analytical epidemiology in this example will be like what will cause diarrhea in children under 3 years of age and what will protect children under 3 years of age form this diarrhea

There was an inverse relationship between duration of breastfeeding and diarrhoea among children under 3 years of age in the Cape Coast Metropolis.
so what will protect such children from diarrhea and what will cause such children to have diarrhea

Question 9

What is seen as anything that affects the well-being of a population?

What describes the distribution and determinants of a particular disease?

Answer 9

• Health-related states or events
• Is seen as anything that affects the well-being of a population.

It includes: communicable diseases and non-communicable infectious diseases, chronic discases, injuries, birth defects, maternal-child health, and behaviors related to health and well-being, such as amount of exercise etc.
• The “epidemiology of a particular disease” describes the distribution and determinants of that particular disease.

Question 10

Below are four key terms taken from the definition of epidemiology, followed by a list of activities that an epidemiologist might perform. Match the term to the activity that best describes it. You should match only one term per activity.
A. Distribution
B. Determinants
C. Application
1. Compare food histories between persons with Staphylococcus food poisoning and those without
2. Compare frequency of brain cancer among anatomists with frequency in gencral population
3. Mark on a map the residences of all children born with birth defects within 2 miles of a hazardous waste site
4. Graph the number of cases of congenital syphilis by year for the country

Explain your answers

Answer 10

1.B. Cuz there is a cause in the activity. The cause is staph food poisoning
2. A cuz you’re looking at frequency
3.A cuz birth defect is the health event or condition and the cause is the hazardous waste site,time is within 2 miles. (Person,place and time)
4.A

Distribution is the frequency and pattern. Pattern is person place and time(recheck)

Here is the correct matching of the key terms with the activities:

1. Compare food histories between persons with Staphylococcus food poisoning and those without
   
   • B. Determinants
   • This activity involves identifying factors (food histories) that may be associated with an increased risk of Staphylococcus food poisoning.
2. Compare frequency of brain cancer among anatomists with frequency in the general population
   
   • A. Distribution
   • This activity involves analyzing the distribution of brain cancer cases in two different populations (anatomists vs. the general population).
3. Mark on a map the residences of all children born with birth defects within 2 miles of a hazardous waste site
   
   • A. Distribution
   • This activity describes the geographic distribution of cases (children with birth defects) around a specific location.
4. Graph the number of cases of congenital syphilis by year for the country
   
   • A. Distribution
   • This activity involves displaying the distribution of congenital syphilis cases over time.

It seems there may be some confusion because more than one activity seems related to “distribution.” However, the key is in understanding that activities like mapping or graphing involve distribution (patterns and frequencies in populations), while comparing histories or examining frequencies between populations can involve determinants or distribution.

In epidemiology, “application” would typically refer to using findings from such studies to create interventions or public health measures, which isn’t directly described by the activities provided.

Yes, you’re on the right track with your thinking! Graphing the number of cases of congenital syphilis by year for the country is indeed an example of distribution rather than application.

Here’s why:

• Distribution in epidemiology refers to describing the occurrence of diseases or health events by time, place, and person. Graphing cases by year involves looking at the time aspect of distribution to understand trends over time.
• Application would involve using the results of such a graph (or other epidemiological studies) to implement public health actions, policies, or interventions. For example, after graphing congenital syphilis cases, an epidemiologist might decide to increase public awareness campaigns or improve prenatal care screenings. The application is the actionable step that follows the analysis.

So, because the graph is focused on the time distribution of the cases, it is considered a distribution activity, not an application. Your understanding is correct: since it involves place (country) and time (year), it fits the definition of distribution.

Question 11

What is application in epidemiology and state the types

Answer 11

In epidemiology, “application” refers to the practical use or implementation of epidemiological principles, methods, and findings to address public health issues. It involves the following key aspects:

1. Intervention Implementation: Applying epidemiological knowledge to implement interventions aimed at preventing or controlling diseases. This can include vaccination programs, health education campaigns, environmental modifications, or policy changes based on epidemiological evidence.
2. Evaluation of Interventions: Assessing the effectiveness and impact of public health interventions using epidemiological methods. This includes measuring outcomes such as disease incidence or prevalence before and after interventions to determine their success in achieving health goals.
3. Health Policy Development: Using epidemiological data to inform the development of health policies and guidelines at local, national, or global levels. This can involve recommending strategies based on epidemiological evidence to improve population health outcomes.
4. Health Services Planning: Applying epidemiological findings to plan and allocate resources for healthcare services. This may involve identifying high-risk populations, forecasting disease burden, and ensuring healthcare services are adequately equipped to respond to health needs based on epidemiological data.
5. Research and Surveillance: Conducting epidemiological research to generate new knowledge about disease patterns, risk factors, and health outcomes. Surveillance systems are also a crucial application, monitoring disease trends over time to detect outbreaks, assess disease burden, and guide public health responses.

In essence, the application of epidemiology involves using scientific evidence and methodologies to intervene, evaluate, inform policy, plan services, conduct research, and monitor health events to improve public health outcomes and reduce disease burden in populations.

Question 12

Who is the father of epidemiology?
What did this father do to be recognized?
Explain the role of epidemiology in eliminating small pox

Answer 12

• Achievements in epidemiology
• John Snow’s work of identifying the source of drinking water as a risk factor for cholera in London in the 19th
century.cholera is feco orally transmitted

• Elimination of small pox in 1978
Role played by epidemiology was providing information about distribution of cases, mechanisms and levels of transmission

What
1
2
3
4

Question 13

How did epidemiology help in the epidemic of methyl mercury

Answer 13

Methylmercury poisoning among people close to Minamata bay, Japan:
Epidemiology helped in the identification of the cause and control of the epidemic(minamata disease)

Question 14

What is measure of disease frequency?
What are the common frequency measures?

Answer 14

This relates to the focus on the occurrence or frequency of disease or risk factors.

Several measures of disease frequency are based on the fundamental concepts of prevalence and incidence.

Common Frequency measures are below; Ratio, Proportion and Rate

Question 15

What is ratio?
What is the formula for ratio?

Answer 15

Ratio is simply one number, a divided by another number, b provided b≠0 i.e a/b or a:b

It is a comparison of any two values. The numerator and the denominator need not to be related. Eg one can compare oranges to apples i.e number of oranges/ number of apples
It can be a comparison between two health events. Example is ratio of people with TB to people with pneumonia

Question 16

What is proportion?
What are the uses of proportion

Answer 16

Proportion is a special ratio in which the numerator, a is part of the denominator, (a+b) and can therefore be expressed as a/(a+b), where (a+b)≠0. But in rate, the numerator and denominator don’t need to be related.

Certainly! In epidemiology, proportions are frequently used to express the frequency or prevalence of a particular health condition or outcome relative to the total population at risk. Here’s an example using the definition you provided:

Example Scenario:

An epidemiologist is studying the prevalence of smoking among adolescents in a school district. They survey a random sample of 800 students and classify their smoking status as follows:

• 200 students report currently smoking cigarettes.
• 600 students report not smoking cigarettes.

Calculation of Proportion:

The proportion of students who currently smoke cigarettes in the surveyed population can be calculated using the formula:

{Proportion of smokers} = {Number of smokers}/{Total number of students surveyed}

Applying the provided formula {a}/{a+b}:

{Proportion of smokers} = {200}/{200 + 600}

{Proportion of smokers} = {200}/{800}

{Proportion of smokers} = 0.25

Interpretation:
In this example, the proportion of students who currently smoke cigarettes in the surveyed population is 0.25 or 25%. This means that 25% of the students sampled reported smoking cigarettes at the time of the survey. This proportion provides an estimate of the prevalence of smoking in the school district population and can be used to assess the magnitude of the health behavior (smoking) within this group.

Proportions in epidemiology are useful for comparing groups, monitoring trends over time, and assessing the distribution of health-related behaviors or conditions within populations.

Question 17

What is rate? Give two examples of rate
How is rate different from proportion

Answer 17

Rate is a measure of the frequency with which an event occurs in a defined population over a specified period of time. It describes how quickly disease occurs in a population
• It is a special ratio which can be expressed by two dissimilar quantities or two distinct descriptions with the same unit but may or may not be a proportion.
Examples
• Number of HIV infected infants in 2003/Number of births in 2003
• Number of lung cancer cases in factory X/Total person-years of exposure
• Number of cervical cancer cases in 2012/Number of women at risk in 2012

Alright, imagine we’re talking about how many people get sick with a cold in your whole school over a year.

• Rate: It’s like saying how many kids got sick out of every 100 kids in your school. For example, if 5 kids out of every 100 got sick, we’d say the rate is 5%.
• Proportion: This is like saying how many kids out of all the kids who got sick actually had a cold. So, if there were 50 sick kids and 30 had a cold, then the proportion of colds would be 30 out of 50, which is 60%.

So, the rate tells us how many out of a certain number are affected overall, while the proportion tells us how many in a group of sick people have a specific condition, like having a cold versus something else.

Or I apologize for the confusion. Let’s clarify the difference between rate and proportion using your examples:

Examples for Rate:

1. Number of HIV infected infants in 2003 / Number of births in 2003:
   • Rate Explanation: This calculates how many infants were born with HIV for every 100 births in a specific year (2003). It focuses on the frequency of HIV infections relative to the total number of births.
2. Number of lung cancer cases in factory X / Total person-years of exposure:
   • Rate Explanation: This measures the occurrence of lung cancer cases per unit of exposure time (person-years) in a specific factory. It shows how often lung cancer happens relative to the time people spend working in that environment.
3. Number of cervical cancer cases in 2012 / Number of women at risk in 2012:
   • Rate Explanation: This tells us how many women were diagnosed with cervical cancer for every group of women who could potentially get it in a specific year (2012). It focuses on the frequency of cervical cancer cases relative to the number of women at risk.

Difference from Proportion:

• Rate: In each of these examples, a rate measures how often a specific event (HIV infection, lung cancer cases, cervical cancer cases) occurs relative to some measure of exposure or risk over a period of time. Rates use a standardized unit (like per 100 births, per 1,000 person-years, per 1,000 women at risk) to make comparisons meaningful across different populations or time periods.
• Proportion: A proportion, on the other hand, compares a part of a group to the whole group itself. It shows the fraction or percentage of a specific subgroup within a larger group. For example, the proportion of HIV-infected infants among all infants born in 2003, or the proportion of cervical cancer cases among all women at risk in 2012.

Key Differences:

• Rate: Focuses on how often an event occurs relative to a specific population size or exposure time. It uses the same unit (e.g., per year, per person) for comparison.
• Proportion: Shows what fraction or percentage of a specific group is affected by a condition or event within the entire group. It doesn’t necessarily use the same unit but compares a part to the whole within a defined subset of the population.

In summary, rates in epidemiology provide a measure of frequency or intensity of events relative to population size or exposure time, while proportions indicate the fraction or percentage of a subgroup within a larger group affected by a specific condition or event. Each serves a distinct purpose in epidemiological analysis and helps to understand disease occurrence and distribution within populations.

Question 18

In epidemiology, what two types of rates do we calculate for ?

Answer 18

Prevalence and incidence rates

Question 19

What is prevalence rate?
How is prevalence calculated?

Answer 19

Prevalence rate: The prevalence of a disease is the number of existing cases among a defined population at a specific point in time.

The prevalence, P is calculated as

P=(Number of people with the disease at the specified time/ Number of people in the population at risk at the specified time(so people exposed to the disease or at risk of the disease but don’t have the disease at that particular time) )* 10n
, n=positive integer
n is usually 2 because we usually express prevalence as a percentage. So 10 to the power 2 is 100.

Certainly! Prevalence rate is a common measure used in epidemiology to assess how widespread a particular disease or condition is within a population at a specific point in time. Here’s an example to illustrate prevalence rate:

Example: Prevalence Rate of Diabetes

Suppose we want to determine the prevalence rate of diabetes in a city during the year 2023.

• Number of people diagnosed with diabetes in 2023: 5,000
• Total population of the city in 2023: 100,000

Calculation of Prevalence Rate:

The prevalence rate of diabetes in the city can be calculated using the formula:

[ \text{Prevalence Rate} = \frac{\text{Number of people with diabetes}}{\text{Total population}} \times 100

[ \text{Prevalence Rate} = \frac{5,000}{100,000} \times 100 ]

[ \text{Prevalence Rate} = \frac{5,000}{1,000} ]

[ \text{Prevalence Rate} = 5\% ]

Interpretation:

In this example, the prevalence rate of diabetes in the city during 2023 is 5%. This means that 5% of the population, or 5 out of every 100 people, were diagnosed with diabetes at some point during that year.

Key Points:

• Definition: Prevalence rate measures the proportion of individuals in a population who have a specific disease or condition at a particular time.
• Usage: It helps to understand the burden of a disease within a population and can be used to compare disease prevalence across different populations or over time.
• Calculation: It is calculated by dividing the number of individuals with the disease by the total population and multiplying by 100 to express it as a percentage.

Prevalence rate provides important insights into the public health impact of diseases and guides healthcare planning and resource allocation strategies accordingly.

Question 20

Explain the types of prevalence
State two key points about point prevalence
Which is used for assessing immediate disease burden in a population?
Which does not take into account the duration of the disease?

Answer 20

Types of prevalence

Point prevalence rate: (It is the number of existing cases at one point in time/ Number of persons in the population at risk at that point in time)*10n

Period prevalence rate: (Total number of people who get the disease at any time during the specified period/ population at risk midway through the period)*10n

Certainly! Let’s explain point prevalence and period prevalence rates with examples:

1. Point Prevalence:

Definition: Point prevalence refers to the proportion of individuals in a population who have a particular disease or condition at a specific point in time.

Example of Point Prevalence:

Imagine we want to determine the point prevalence of asthma in a school on a particular day.

• Number of students diagnosed with asthma on a specific day: 20
• Total number of students in the school: 500

Calculation of Point Prevalence:

Point prevalence is calculated as:

[ \text{Point Prevalence} = \frac{\text{Number of individuals with the disease at a specific point in time}}{\text{Total population}} \times 100 ]

[ \text{Point Prevalence} = \frac{20}{500} \times 100 ]

[ \text{Point Prevalence} = 4\% ]

Interpretation:

In this example, the point prevalence of asthma in the school on that specific day is 4%. This means that on that particular day, 4% of the students were diagnosed with asthma.

Key Points about Point Prevalence:

• It provides a snapshot of disease prevalence at a single moment in time.
• It is useful for understanding the immediate burden of a disease in a population but period prevalence assess disease burden over time.
• It does not take into account the duration of the disease.

Point prevalence is the proportion of a population that has a specific disease or condition at a single point in time. It gives a “snapshot” of how widespread a disease is right now, without considering how long people have had the disease.

•	Point prevalence does not account for the duration of the disease because it only considers who has the disease at that exact moment—whether someone has had the disease for a day or for ten years doesn’t matter in this calculation. It only tells us “how many” people are currently affected, not “for how long” they have been affected.
•	For example, if you’re measuring point prevalence on a particular day, you count all people who have the disease on that day, but you don’t track when they got sick or how long they’ve been sick.

To understand the impact or burden of a disease over time, you would look at period prevalence or other measures that include duration, like the incidence rate

2. Period Prevalence:

Definition: Period prevalence refers to the proportion of individuals in a population who have a particular disease or condition over a specified period of time.

Example of Period Prevalence:

Now, let’s consider the period prevalence of diabetes in a community over a year.

• Number of individuals diagnosed with diabetes during the year: 1,000
• Total population of the community: 50,000

Calculation of Period Prevalence:

Period prevalence is calculated as:

[ \text{Period Prevalence} = \frac{\text{Number of individuals with the disease during a specified period}}{\text{Total population}} \times 100 ]

[ \text{Period Prevalence} = \frac{1,000}{50,000} \times 100 ]

[ \text{Period Prevalence} = 2\% ]

Interpretation:

In this example, the period prevalence of diabetes in the community over the year is 2%. This means that over the course of the year, 2% of the population was diagnosed with diabetes at some point.

Key Points about Period Prevalence:

• It provides an understanding of the cumulative burden of a disease over a specified period.
• It considers the duration of the disease within the defined time frame.
• It is useful for studying chronic conditions or diseases with long durations.

Summary:

• Point prevalence reflects the proportion of individuals with a disease at a specific moment.
• Period prevalence reflects the proportion of individuals with a disease over a specified period of time.

Point Prevalence: Provides a snapshot of disease occurrence at a specific moment in time (e.g., a particular hour,day).
• Period Prevalence: Indicates disease occurrence over a specified period (e.g., a decade,year,semester ), capturing individuals diagnosed with the disease at any time during that period.

These examples illustrate how prevalence measures can vary based on the time frame considered, providing insights into disease patterns within populations over different durations or specific points in time.

These measures are essential in epidemiology for assessing disease burden, planning healthcare resources, and understanding the impact of diseases within populations.

You’re right to notice that both point prevalence and period prevalence can cover a specific timeframe, and understanding the difference between the two can sometimes be confusing. Here’s how to differentiate them:

• Point Prevalence focuses on a specific point in time, even if that “point” is described broadly (e.g., “a particular day,” “a specific month,” or “a particular year”). It tells us the proportion of a population that has a disease or condition at that exact point in time.
• Period Prevalence covers a duration of time (e.g., a week, a month, a year) and accounts for everyone who had the disease at any time during that period. It includes both new cases and existing cases throughout that timeframe.

1. Point Prevalence Example:
   
   • If we say the point prevalence of diabetes in 2024 in a town is 8%, this means that 8% of the population had diabetes on a specific day or point in 2024 (e.g., January 1st, or July 1st). The idea is that it provides a “snapshot” of who had the condition on that particular day, even if we use a broader label like “2024.”
2. Period Prevalence Example:
   
   • If we talk about the period prevalence of flu during the month of March 2024, this means we are considering everyone who had the flu at any point in March—whether they got it on March 1st, recovered by March 10th, or developed it on March 15th and still had it by March 31st. Period prevalence tells us the total percentage of people affected throughout the entire month.

• If you’re only looking at who is affected at a specific point, regardless of how broad or narrow that point is defined (e.g., “January 1st” or “a specific day in 2024”), it’s point prevalence.
• If you’re considering the entire timeframe and capturing everyone affected at any time during that period (e.g., “the whole month of January” or “during the year 2024”), it’s period prevalence.

• Point Prevalence: “On January 1st, 5% of the population had the flu.” (Snapshot)
• Period Prevalence: “In the year 2024, 20% of the population had the flu at some point.” (Duration)

The main difference is whether you are looking at a specific point in time or considering a range where cases can come and go.

Question 21

Example:
In a survey of 1,150 women who gave birth in Maine in 2000, a total of 468 reported taking a multivitamin at least 4 times a week during the month before becoming pregnant. Calculate the prevalence of frequent multivitamin use in this group.
What kind of prevalence is being calculated for here and why do you think it’s that type of prevalence

Answer 21

• Numerator = 468 multivitamin users
• Denominator = 1,150 women
• Prevalence = (468 / 1,150) x 100 = 0.407 x 100 = 40.7%

You’re right that 2000 is a year, and it might seem like a period. However, in the context of the scenario provided, the distinction lies in how we interpret the timeframe:

1. Point Prevalence:
   
   • This measures the proportion of individuals with a condition or characteristic at a specific point in time. For your scenario, if the data collected is from a single point in time (e.g., the prevalence of multivitamin use among women who gave birth in 2000), it is considered point prevalence.
   • Example: The percentage of women using multivitamins at any moment during the year 2000.
2. Period Prevalence:
   
   • This measures the proportion of individuals with a condition or characteristic over a defined period of time, which could be longer than a single moment.
   • Example: If the study had asked about multivitamin use over the entire year leading up to the birth (e.g., during the 12 months before conception), it would be considered period prevalence.

In your scenario:
- Survey of 1,150 women who gave birth in Maine in 2000: The data does not specify that it was collected over the entire year or during a specific period before birth. If the survey was conducted at one point in time (e.g., at the end of 2000), it would be considered point prevalence.

If the data were to specifically address the period before conception (such as frequent use during the year before conception), it would be period prevalence. However, if it simply notes that 468 out of 1,150 women reported using multivitamins frequently at a given moment in 2000, this reflects point prevalence.

If the survey asked about multivitamin use during the entire year before becoming pregnant (i.e., a defined period), the prevalence calculated would be period prevalence. If the survey is simply a snapshot from the year 2000 without specifying a period of observation before the survey, it’s point prevalence.

Question 22

State five factors that influence prevalence rate (rate at which people get a disease)

Answer 22

Factors influencing increased prevalence rate:
Longer duration of the disease- if disease isn’t controlled, more people will develop it. Also, As patients live longer with the disease, they remain part of the pool of individuals counted in the prevalence calculation over time. For example, if a person is diagnosed with diabetes at age 40 and lives with it for 30 years, they contribute to the prevalence rate count for all those 30 years.

Prolonged life of patients without cure-Advances in medicine may help manage symptoms and prolong life, but without a cure, patients continue to be counted in prevalence calculations indefinitely. This results in a cumulative increase in the number of people living with the disease at any given time.

Increase in the number of new cases (i.e incidence)-A higher incidence rate (number of new cases) adds to the existing pool of people with the disease, increasing prevalence over time

In-migration of cases-Migration of individuals already diagnosed with the disease into a population increases the number of cases in that population, contributing to higher prevalence.

Out-migration of healthy people-Migration of healthy individuals out of a population decreases the denominator (total population), which can artificially inflate the prevalence rate if the number of cases remains the same.

Improved diagnostic facilities (better reporting)-Enhanced ability to diagnose and report cases more accurately leads to better detection of the disease, increasing the reported prevalence rate.

In-migration of people who are susceptible to this disease-Migration of individuals who are susceptible to the disease into a population can increase the number of new cases, thereby increasing prevalence.

These factors highlight how changes in disease dynamics, population movement, healthcare capabilities, and disease management can impact the prevalence rate of diseases within a population over time.

Question 23

State six factors influencing decreased prevalence rate

Answer 23

Shorter duration of the disease-Diseases with shorter durations mean individuals recover quickly or the disease resolves on its own, reducing the number of people living with the disease at any given time and thereby decreasing prevalence.

High case-fatality for the disease-Diseases with high case-fatality rates mean a larger proportion of diagnosed individuals do not survive the disease. This reduces the number of people who remain alive and counted in the prevalence calculation.

Decline in the number of new cases (i.e incidence)-A decrease in the incidence rate (number of new cases) means fewer new individuals are added to the pool of people with the disease, leading to a decrease in prevalence over time.

In-migration of healthy people-Migration of healthy individuals into a population increases the denominator (total population), which can lower the prevalence rate if the number of cases remains the same.

Out-migration of cases-Migration of individuals already diagnosed with the disease out of a population decreases the number of cases in that population, resulting in a lower prevalence rate if the total population remains stable.

Improved cure rate of cases-Advances in treatment that improve the cure rate of the disease mean more individuals recover from the disease and are no longer counted in the prevalence calculation, leading to a decrease in prevalence.

Question 24

What is the essence of prevalence rate
Between prevalence rate and incidence rate, which tells us how many people have had a disease for sometime and those who were recently diagnosed?
Between prevalence rate and incidence rate, which is Usually used to measure the occurrence of conditions or diseases for which the onset may be gradual?
Between incidence and prevalence rate, which checks disease burden ?

Answer 24

Essence of prevalence rate
Usually used to measure the occurrence of conditions or diseases for which the onset may be gradual. Eg diabetes: Captures Ongoing Burden: Diabetes is a chronic condition where individuals live with the disease for years. The prevalence rate tells us how many people in the community are currently affected by diabetes. This includes those who have had the disease for some time and those who were recently diagnosed.

The measure usually used to assess the occurrence of conditions or diseases with a gradual onset is the prevalence rate.

• Prevalence rate refers to the proportion of individuals in a population who have a specific condition or disease at a particular point in time or over a specific period. It is ideal for measuring diseases with a gradual onset (e.g., diabetes, hypertension) because it captures both new and existing cases, providing a snapshot of how widespread a condition is in a population.
• Incidence rate, on the other hand, measures the number of new cases of a disease that develop in a population during a specific time period. It is more suited for diseases with a sudden onset or for studying the risk of developing a disease over time.

Thus, for conditions where the onset is gradual and the disease persists over time, the prevalence rate is the more appropriate measure.

Imagine you have a school playground where some kids are wearing hats. Every day, more kids start wearing hats, but some have been wearing them for a long time, and some just started wearing them recently.

• Prevalence rate is like counting how many kids are wearing hats on the playground right now. It doesn’t matter if they started wearing the hat a long time ago or just today; we just count everyone wearing a hat at this moment.
• This is perfect for diseases that take a long time to show up, like diabetes, because it tells us how many people have the disease at any given time—whether they got it last year or just recently.

So, for slow-starting things like some diseases, we use the prevalence rate because it shows us the total number of people who have it, not just the new ones. It helps us see the “big picture” of how common the disease is.

•	 Helpful in the planning in health services: Useful for Healthcare Planning: Knowing that 10% of the population has diabetes helps healthcare planners understand the ongoing need for diabetes management services, such as regular check-ups, medication, and education programs. It guides them in estimating the number of healthcare professionals needed, the frequency of medical supplies required, and the provision of educational resources for managing the condition. Helpful in assessing the needs of health services: so you’ll access current health services and see if they have the capacity to combat the prevalence rate of a particular disease. Whether it’s high or not. If high, then you bring more resources to the health services

Question 25

What is incidence rate
Another name for incidence rate is what?
What is the difference between incidence density and incidence proportion

Practice MCQs

1. Question 1:
   
   • “In a study of 1,000 people, 100 developed a disease over a year. What measure is calculated by dividing 100 by 1,000?”
     
     • A) Incidence Rate
     • B) Prevalence
     • C) Cumulative Incidence
     • D) Mortality Rate
2. Question 2:
   
   • “In a cohort study, there were 50 new cases of a disease, and the total person-time at risk was 2,500 person-years. What is this measure called?”
     
     • A) Incidence Rate
     • B) Prevalence
     • C) Cumulative Incidence
     • D) Risk Ratio

. Here are five medium to hard multiple-choice questions (MCQs) on the differences between incidence rate and cumulative incidence, focusing on their definitions, uses, and implications related to risk and follow-up.

A. Determining the risk of developing diabetes over a 5-year period in a group where all participants are followed for the entire duration.
B. Calculating the speed at which new flu cases appear in a community where people move in and out frequently.
C. Estimating the number of car accidents occurring per 1,000 miles driven by all cars in a city.
D. Measuring the rate of new tuberculosis cases in a population with varying lengths of follow-up due to emigration.

**
### 2. A study follows 200 individuals for a year to measure the occurrence of a rare disease. If 10 individuals develop the disease during this period, what is the cumulative incidence?

A. 2 cases per 100 person-years
B. 5%
C. 10 cases per 1,000 person-years
D. 50%

**

A. It assumes that all individuals are followed up for the same amount of time.
B. It is more appropriate than cumulative incidence when some participants drop out or are lost to follow-up.
C. It represents the total number of new cases in the population during the entire study period.
D. It is calculated only when the outcome being studied is common.

**
### 4. Which of the following is true about cumulative incidence but not about incidence rate?

A. It accounts for differing amounts of follow-up time among study participants.
B. It is used to estimate the risk of developing a disease over a defined period in a closed cohort.
C. It provides information on how quickly new cases of a disease occur in a population.
D. It adjusts for the fact that people enter and leave the population over time.

A. Incidence rate, because it reflects how fast new cases are occurring and adjusts for different follow-up times.
B. Cumulative incidence, because it reflects the overall risk and assumes all participants are followed for the entire period.
C. Prevalence rate, because it measures the proportion of new cases within a fixed time period.
D. Point prevalence, because it captures the exact number of cases at a single point in time.

Answer 25

Incidence rates (or incidence): new people who developed a condition over a particular period of time
Perrson-time rate or incidence rate (incidence density) of a disease , I is given by
I=(Number of new cases in a specified period/sum of the length of time during which each person in the population is at risk)*10n

Time in the denominator above could be days, months or years

Cumulative incidence (Incidence proportion or attack rate or the risk ), CI on the other hand is calculated by
CI=(Number of new cases in a specified period/Number of people free of the disease in the population at risk at the beginning of the period)*10n

Sure, let’s use an example with a disease to explain both concepts:

Incidence Density (Rate):

Imagine you have a class with 20 friends. They all love playing outside every day. One day, 5 friends catch a cold. The next day, 3 more friends catch it. Incidence density is like counting how many friends get the cold each day.

• Example: If you watch them for 5 days and count a total of 10 friends who caught a cold, incidence density would be how many friends caught a cold each day on average.

Incidence Proportion (Cumulative Incidence):

Now, imagine you want to know how many friends caught the cold in total over the 5 days.

• Example: Out of the 20 friends, if 8 friends caught the cold by the end of the 5 days, the incidence proportion would be how many friends got the cold out of all the friends.

Key Difference:

• Time Focus: Incidence density looks at how many friends get sick each day (like counting how many catch a cold each day). Incidence proportion looks at how many friends get sick in total over the whole time (like counting how many catch a cold over all 5 days).

In simple terms, incidence density tells us how fast friends are getting sick each day, while incidence proportion tells us how many friends got sick in total over all the days we counted.

Yes, both cumulative incidence and incidence rate calculate new cases, but they do so in different ways and are used in different contexts. Here’s a breakdown of the differences:

• Definition: The proportion of a population that develops a condition (new cases) over a specified period.
• Formula:
  [
  \text{Cumulative Incidence} = \frac{\text{Number of New Cases during the Period}}{\text{Number of Individuals at Risk at the Start of the Period}}
  ]
• Measurement: Expressed as a proportion (e.g., 10%) or per 1,000 individuals.
• Context: Used when you follow a fixed population over a period of time and want to know the probability of developing the disease.
• Example: If 50 new cases of a disease occur in a population of 1,000 people over one year, the cumulative incidence is:
  [
  \frac{50}{1000} = 0.05 \text{ or } 5\%
  ]

• Definition: The rate at which new cases of a condition occur in a population per unit of person-time.
• Formula:
  [
  \text{Incidence Rate} = \frac{\text{Number of New Cases}}{\text{Total Person-Time at Risk}}
  ]
• Measurement: Expressed as cases per person-time (e.g., per person-year).
• Context: Used when individuals in the population are followed for different lengths of time, and you want to account for the varying time at risk.
• Example: If 50 new cases of a disease occur over 1,000 person-years, the incidence rate is:
  [
  \frac{50}{1000 \text{ person-years}} = 0.05 \text{ per person-year}
  ]

1. Population at Risk:
   
   • Cumulative Incidence: Considers the initial number of individuals at risk.
   • Incidence Rate: Considers the total person-time at risk.
2. Time Frame:
   
   • Cumulative Incidence: Does not account for the varying times individuals are at risk; it’s a simple ratio.
   • Incidence Rate: Accounts for the varying follow-up times among individuals.
3. Use Case:
   
   • Cumulative Incidence: Best for fixed populations over a defined period.
   • Incidence Rate: Best for dynamic populations or when individuals are followed for different lengths of time.

Suppose you are studying a disease in a population over one year.

Cumulative Incidence:
- You start with 1,000 people at the beginning of the year.
- By the end of the year, 50 new cases are diagnosed.
- Cumulative incidence:
[
\frac{50 \text{ new cases}}{1000 \text{ people}} = 0.05 \text{ or } 5\%
]

Incidence Rate:
- In the same population, some individuals may leave the study early, and new individuals may join, contributing different amounts of person-time.
- Suppose the total person-time at risk is 900 person-years (taking into account the varying follow-up times).
- Incidence rate:
[
\frac{50 \text{ new cases}}{900 \text{ person-years}} = 0.056 \text{ per person-year}
]

###

Understanding the differences between incidence rate (or person-time rate/incidence density) and cumulative incidence (or incidence proportion/risk) involves recognizing how each measure accounts for time and population dynamics. Here’s a breakdown of these concepts:

• Definition: The incidence rate, also known as incidence density or person-time rate, measures the rate at which new cases of a disease occur in a population over time. It considers the amount of time each person in the study was at risk for developing the disease.
• Calculation: This is typically expressed as the number of new cases per unit of person-time (e.g., per 1,000 person-years).Formula:
  [
  \text{Incidence Rate} = \frac{\text{Number of New Cases}}{\text{Total Person-Time at Risk}}
  ]
  • Person-Time: This is the sum of the time each person in the study is observed and at risk for the disease. For instance, if one person is observed for 2 years and another for 3 years, the total person-time is 5 person-years.
• Why Time Matters: Incidence rate accounts for the varying lengths of time individuals are at risk. It is particularly useful when the population is dynamic (i.e., people enter and leave the study at different times) or when follow-up times vary.

• Definition: Cumulative incidence, also known as incidence proportion or risk, measures the proportion of a population that develops the disease over a specified period. It provides a snapshot of the risk of developing the disease in a given period.
• Calculation: This is calculated as the number of new cases of a disease divided by the number of individuals at risk at the beginning of the period, usually expressed as a percentage.Formula:
  [
  \text{Cumulative Incidence} = \frac{\text{Number of New Cases}}{\text{Number of Individuals at Risk at Start}}
  ]
• Why It Differs: Cumulative incidence does not account for varying follow-up times or population dynamics. It assumes that everyone is at risk for the entire period of observation. It is useful for understanding the overall risk of disease in a population over time but does not provide information about the rate of disease occurrence.

1. Time Consideration:
   
   • Incidence Rate: Takes into account the time each person was at risk, making it suitable for studies where follow-up time varies.
   • Cumulative Incidence: Assumes a fixed period of observation for all individuals, regardless of how long each person was actually at risk.
2. Population Dynamics:
   
   • Incidence Rate: Can handle situations where the population changes over time (e.g., people entering or leaving the study).
   • Cumulative Incidence: Assumes a stable population throughout the observation period.
3. Measurement Type:
   
   • Incidence Rate: Expressed as cases per unit of person-time (e.g., cases per 1,000 person-years).
   • Cumulative Incidence: Expressed as a proportion or percentage of the initial population at risk.

• Incidence Rate: In a study where 10 new cases occur in 1,000 person-years, the incidence rate is 10 cases per 1,000 person-years. If the follow-up time varies among participants, this measure accounts for that variation.
• Cumulative Incidence: If a population of 1,000 individuals is followed for 5 years and 100 new cases are observed, the cumulative incidence is 100/1,000 = 0.1 or 10%. This measure provides the overall risk of developing the disease during the 5-year period, without considering individual follow-up times.

In summary, incidence rate is about time and provides a more dynamic measure of disease occurrence, while cumulative incidence gives a snapshot of risk over a specified period without considering variations in follow-up time.

he term “incidence density” is used to describe the incidence rate because it reflects how new cases of a disease are distributed over time in a population. Here’s why the term “density” is applicable:

1. Concept of Density:• Density: In general, density refers to how something is distributed over a certain space or volume. For example, in physical sciences, density might refer to mass per unit volume. In epidemiology, density relates to how often new cases occur per unit of person-time.
2. Incidence Density (Incidence Rate):• Definition: Incidence density measures the rate at which new cases of a disease occur per unit of person-time. Person-time is the total time that all individuals in a study population are at risk.
   Formula:

\text{Incidence Density} = \frac{\text{Number of New Cases}}{\text{Total Person-Time at Risk}}

•	How Density Applies:
•	Person-Time as a Denominator: Incidence density uses person-time (e.g., person-years) as the denominator, which allows it to account for varying follow-up times among individuals. For instance, if one individual is followed for 2 years and another for 3 years, the total person-time is 5 person-years.
•	Rate Per Unit Time: The term “density” reflects that this measure evaluates the frequency (rate) of new cases occurring per unit of time, essentially giving a “density” of disease occurrence over the time each person was at 

No worries—I’ll explain it more clearly! Let’s simplify the concepts of incidence rate and cumulative incidence and focus more on how they relate to risk and following up over time.

Imagine a classroom where we are trying to see how many students catch a cold over a school year. We want to measure how often new colds happen and understand the risk of getting a cold.

• What It Is: Cumulative incidence tells us the risk of a student getting a cold during the whole school year.
• How It Works: At the beginning of the year, there are 100 students. If, by the end of the year, 20 students have caught a cold, the cumulative incidence is 20 out of 100, or 20%. This means there is a 20% chance that any student in the class will get a cold by the end of the year.
• Why It’s About Risk: It shows the overall risk of getting sick in that group over the entire time (the whole school year). Everyone is watched the whole time, from start to finish.
• When It Works Best: This is useful when we can follow everyone for the whole period, like tracking all 100 students for the entire year. If some students leave the school halfway, it doesn’t work as well because we lose track of their health status.

• What It Is: Incidence rate tells us how quickly new colds are happening in the class, considering the time each student is at risk.
• How It Works: If 5 students catch a cold over 100 student-months (meaning, if we add up all the months that each student is at risk), the incidence rate would be “5 colds per 100 student-months.” This means we’re looking at how fast new colds are occurring, considering the exact amount of time each student was “at risk” of getting a cold.
• Why It’s About Follow-Up: It’s useful when not all students stay in the school for the entire year. Maybe some students move away, or some join late. We still want to measure how fast new colds are happening, even if we don’t have the same follow-up time for everyone.
• When It Works Best: Incidence rate is useful when people don’t all stay for the same amount of time. It adjusts for those differences by looking at “person-time,” like counting the exact time each student is around and at risk.

• Cumulative Incidence focuses on the risk over a set period, and it works best if everyone is followed for the same amount of time (e.g., all students are followed for the whole year).
• Incidence Rate focuses on the speed of new cases and can handle situations where people (or students) are followed for different amounts of time. It adjusts for varying follow-up times.

• Cumulative Incidence: Good for measuring the risk over a fixed time if we can follow everyone the whole time.
• Incidence Rate: Good for measuring the rate of new cases when some people (or students) might drop out or join late. It gives a fair picture even with different follow-up times.

Does this help clarify how these terms relate to risk and following up?

Here are five medium to hard multiple-choice questions (MCQs) on the differences between incidence rate and cumulative incidence, focusing on their definitions, uses, and implications related to risk and follow-up.

A. Determining the risk of developing diabetes over a 5-year period in a group where all participants are followed for the entire duration.
B. Calculating the speed at which new flu cases appear in a community where people move in and out frequently.
C. Estimating the number of car accidents occurring per 1,000 miles driven by all cars in a city.
D. Measuring the rate of new tuberculosis cases in a population with varying lengths of follow-up due to emigration.

Answer: A. Determining the risk of developing diabetes over a 5-year period in a group where all participants are followed for the entire duration.

A. 2 cases per 100 person-years
B. 5%
C. 10 cases per 1,000 person-years
D. 50%

Answer: B. 5%

A. It assumes that all individuals are followed up for the same amount of time.
B. It is more appropriate than cumulative incidence when some participants drop out or are lost to follow-up.
C. It represents the total number of new cases in the population during the entire study period.
D. It is calculated only when the outcome being studied is common.

Answer: B. It is more appropriate than cumulative incidence when some participants drop out or are lost to follow-up.

A. It accounts for differing amounts of follow-up time among study participants.
B. It is used to estimate the risk of developing a disease over a defined period in a closed cohort.
C. It provides information on how quickly new cases of a disease occur in a population.
D. It adjusts for the fact that people enter and leave the population over time.

Answer: B. It is used to estimate the risk of developing a disease over a defined period in a closed cohort.

A. Incidence rate, because it reflects how fast new cases are occurring and adjusts for different follow-up times.
B. Cumulative incidence, because it reflects the overall risk and assumes all participants are followed for the entire period.
C. Prevalence rate, because it measures the proportion of new cases within a fixed time period.
D. Point prevalence, because it captures the exact number of cases at a single point in time.

Answer: A. Incidence rate, because it reflects how fast new cases are occurring and adjusts for different follow-up times.

These questions should help you understand the nuances between incidence rate and cumulative incidence and how they are applied in different epidemiological scenarios!

Yes, both incidence rate and prevalence can be used for diseases with a gradual onset, but they serve different purposes in understanding the disease dynamics. Let me clarify how each metric is applied and correct any confusion:

1. Incidence Rate:• What It Measures: The incidence rate measures the rate at which new cases of a disease occur in a population over a specified period of time. It focuses on new occurrences and is particularly valuable in understanding how quickly a disease is developing in a population.
   • Suitable for Gradual Onset?
   Yes, incidence rate can be suitable for diseases with a gradual onset (e.g., Type 2 diabetes, Alzheimer’s disease) because it provides insight into how frequently new cases emerge over time. It’s ideal when you want to study the dynamics of new cases and account for the varying follow-up times of individuals (e.g., if participants drop out or die).
   • Key Point: Incidence rate is useful for any condition where tracking the rate of new cases is important, whether the disease has a gradual onset (chronic diseases) or a rapid onset (infectious diseases).
2. Prevalence:• What It Measures: Prevalence measures the total number of cases (both new and existing) of a disease in a population at a specific point in time (point prevalence) or over a period of time (period prevalence). It reflects the burden of a disease in the population.
   • Suitable for Gradual Onset?
   Yes, prevalence is particularly suitable for diseases with a gradual onset that tend to be chronic (e.g., hypertension, chronic kidney disease). Because these diseases often have a long duration, many people may have the disease at any given point in time, which results in high prevalence.
   • Key Point: Prevalence provides a snapshot of how widespread a disease is but doesn’t tell you how quickly new cases are occurring.
3. Clarification on Short vs. Gradual Onset Diseases:• Short Onset Diseases: For diseases with a short or rapid onset (like influenza or food poisoning), incidence rate can quickly capture how new cases emerge over a shorter period. However, prevalence might be less meaningful because people recover or die quickly, resulting in low prevalence despite high incidence.
   • Gradual Onset Diseases: For diseases with a gradual or longer onset, both incidence rate (for new cases over time) and prevalence (for total cases at a point in time) are meaningful:
   • Incidence Rate: Helps track how new cases accumulate, especially over long periods.
   • Prevalence: Shows how many people are currently living with the disease.

Summary:

•	Incidence Rate is used for understanding new case development over time, regardless of whether the onset is short or gradual.
•	Prevalence is more about understanding the current burden of disease at a point in time, often relevant for chronic or gradual onset diseases.

Both incidence rate and prevalence can be used for diseases with gradual onset, but they answer different epidemiological questions. I hope this clears up the confusion!

Question 26

What is the Essence of cumulative incidence

Answer 26

It is suitable for communicating health information to decision-makers

Question 27

Difference between prevalence and incidence rates

Answer 27

Prevalence rate looks at total number of people who have developed a particular condition. Both old and new people
Incidence rate only looks at the new people who have developed the condition

Question 28

Example A: In the study of diabetics, 100 of the 189 diabetic men died during the 13-year follow-up period.
Calculate the risk of death for these men.

Example B: In an outbreak of gastroenteritis among attendees of a corporate pienic, 99 persons ate potato salad, 30 of whom developed gastroenteritis. Calculate the risk of illness among persons who ate potato salad.

Answer 28

Example A answer: we are calculating for incidence proportion which is the same as risk.
Numerator = 100 deaths among the diabetic men
Denominator = 189 diabetic men
10n = 102 = 100
Risk = (100 / 189) x 100 = 52.9%

Example B:

Numerator = 30 persons who ate potato salad and developed gastroenteritis
Denominator = 99 persons who ate potato salad
10n = 102 = 100
Risk = “Food-specific attack rate” = (30 / 99) x 100 = 0.303 x 100 = 30.3%

You’re right to distinguish between a proportion and a percentage, and it’s important to understand how incidence is typically calculated and expressed. Let’s clarify these concepts:

• Proportion: A proportion is a part of a whole, expressed as a fraction or a decimal. For example, if 2 out of 10 people are affected by a disease, the proportion is 2/10 or 0.2.
• Percentage: A percentage is a proportion multiplied by 100. So, a proportion of 0.2 is equivalent to 20%.

• Incidence Proportion (also called Cumulative Incidence) is a measure of the risk of developing a disease over a specified period of time.
• It is calculated by dividing the number of new cases during a specific period by the number of individuals at risk at the start of the period.Formula:
  [
  \text{Incidence Proportion} = \frac{\text{Number of New Cases}}{\text{Population at Risk}} \times 100
  ]For example, if 50 new cases of a disease occur in a population of 1,000 people over a year, the incidence proportion would be:
  [
  \text{Incidence Proportion} = \frac{50}{1000} = 0.05 \text{ (or 5% when expressed as a percentage)}
  ]

• Clarity and Communication: Public health and epidemiology often express incidence proportions as percentages to make the data easier to interpret and communicate. For instance, saying “the incidence proportion is 5%” is often clearer than saying “the incidence proportion is 0.05.”

• Risk: In epidemiology, risk is often expressed as a percentage, representing the chance that an individual will develop the disease over the specified period. When incidence proportion is used as a measure of risk, it is often expressed as a percentage.

So, while a proportion itself is not a percentage, expressing the incidence proportion as a percentage helps to communicate the likelihood (or risk) of developing a disease in a more understandable way. This is why incidence proportion (or cumulative incidence) is often presented as a percentage.

Question 29

What is case fatality rate?
How is it calculated

What is an indicator for the severity of disease in a specified period?

Answer 29

Case-fatality rate is an indicator for the severity of disease in a specified period

Case-fatality rate is usually expressed in percentages and is calculated as:

Case-fatality (%)= (Number of deaths attributed to a specific disease in a specified period/Number of diagnosed cases of the disease within the specified period)*100

Question 30

What is an indicator for the severity of disease in a specified period?
A. Incidence rate

B) Case-fatality rate

C) Prevalence rate

D) Mortality rate

E) Recovery rate

How is the answer calculated
Why is it important

Answer 30

Case-fatality rate is an indicator for the severity of disease in a specified period

Case-fatality rate is usually expressed in percentages and is calculated as:

Case-fatality (%)= (Number of deaths attributed to a specific disease in a specified period/Number of diagnosed cases of the disease within the specified period)*100

The mortality rate is the number of deaths from all causes in a population over a specified period, typically expressed per 1,000 or 100,000 people.
• Purpose: Mortality rate gives a broad measure of overall death in a population but does not specifically relate to the severity of a particular disease. It includes deaths from all causes and does not account for the disease-specific context.
So mortality will be total deaths from every cause in a population divided by total population at risk x 100

Sure, here’s a simple example to explain case fatality rate in epidemiology:

Imagine a school with 50 students. One day, 10 students get sick with a new flu. Out of these 10 students, sadly, 2 students become very ill and pass away.

• Case Fatality Rate Calculation:
  
  • Case Fatality Rate = (Number of deaths from the disease / Number of people diagnosed with the disease) * 100
• Example Calculation:
  
  • In this scenario, the case fatality rate would be: (2 / 10) * 100 = 20%

Explanation:

The case fatality rate tells us how deadly a disease is for those who get sick. In our example, 20% of the students who caught the flu ended up passing away from it. This rate helps epidemiologists and doctors understand the seriousness of a disease and plan how to prevent it or treat it better in the future.

Question 31

There’s a question in a table in the sldies, solve them
The answers are in this card

Answer 31

Incidence of stroke in those who never smoked:

Those who smoked but got stroke is 70
Those who smoked and got stroke is 139
Total population is 100,000

Person time Incidence rate for those who didn’t smoke but got stroke is 70/395,594
= 0.0001769= 17.69 cases per 100,000 persons per year or persons year

Person time Incidence rate for those who smoked and got stroke is 139/280,141
= 0.00049618= 49.61 cases per 100,000 persons per year or persons year

Question 32

Using the fig below estimate the:(the figure is in the slides. The answers are here)

1.point prevalence at year 2

2.person-time incidence rate

3.cumulative incidence

4.Case fatality rate

5.Prevalence at year 6

Answer 32

1.number of people who developed the condition at year 2. So 2 people developed the condition at year 2. Therefore the prevalence at year 2 is 2/7x100=28.57%

Prevalence rate : 3 because over the 7 years,3 people got it.
will be 3/7x100=

2. 3/7 years = 0.4285 person years
3. 3/7x100=42.85%
   4.1/3x100=33.3%
4. 3/7x100=

Question 33

• Number of HIV infected infants in 2003/Number of births in 2003

Is the above example a rate, a ratio or a proportion?

Answer 33

To differentiate between rate and proportion in MCQs, look for these key aspects:

1. Proportion:
   
   • Definition: A proportion is a type of ratio where the numerator is a part of the denominator. It reflects the part-to-whole relationship.
   • Characteristics:
     
     • Compares a subset to the total.
     • Does not necessarily involve time or exposure.
   • Example Question: “What is the proportion of HIV-infected infants among all births in a given year?” (Here, you’re comparing part (HIV-infected infants) to the whole (total births).)
2. Rate:
   
   • Definition: A rate measures the frequency of an event relative to a unit of time or another dimension. It often involves dissimilar quantities and includes a time component.
   • Characteristics:
     
     • Measures events in relation to time or exposure.
     • Often expressed as “per” some unit, like per 1,000 person-years or per year.
   • Example Question: “What is the rate of HIV infection among infants per 1,000 births per year?” (Here, you’re measuring the frequency of infection with a time context.)

How to Identify the Focus in Questions:

1. Check for Time or Exposure:
   
   • Rate: Look for terms like “per year,” “per 1,000 people,” or “per exposure.” These indicate that the question involves a time component or a dimension of exposure.
   • Proportion: If the question is simply comparing part of a population to the whole without additional context or units, it’s likely asking for a proportion.
2. Look for Contextual Clues:
   
   • Rate: Usually involves comparisons involving time or another dimension, like “number of cases per 1,000 people.”
   • Proportion: Involves a straightforward part-to-whole comparison, like “percentage of patients with a condition.”

Example Breakdown:
- Proportion: Number of HIV-infected infants / Total number of births.
- Rate: Number of new cases of a disease per 1,000 person-years or per year.

By analyzing the question’s context and the presence of time or exposure dimensions, you can determine whether to choose rate or proportion.

rate because a rate typically involves a measure of frequency over time or space, often with units that denote time or another dimension. Rates often compare occurrences with a time period or other context, such as “number of new cases per year.”

In your example, you are comparing the number of HIV-infected infants to the total number of births within the same time period (2003), without incorporating a unit of time or another dimension. Thus, it’s a proportion, not a rate.

An example of a rate is the incidence rate of a disease, such as:

Number of new cases of tuberculosis per 100,000 people per year.

Here, the rate is expressed as the number of new cases occurring in a specific population over a specific time period (per year). This measurement involves both the frequency of new cases and a time component.

Number of heart attacks per 1,000 person-years.

In this example, “person-years” accounts for both the number of people and the duration of time they are observed.

Another example of a rate is:

Number of traffic accidents per 1,000 miles driven.

In this case, the rate measures the frequency of traffic accidents relative to the distance traveled, which incorporates a time or distance component into the measurement of occurrences.

It can actually be a rate. A rate measures the frequency of an event occurring in a defined population over a specified time period. It often involves dissimilar quantities (e.g., cases and person-years) and includes a time component.

Question 34

• Number of lung cancer cases in factory X/Total person-years of exposure
Is the above example a rate, ratio or a proportion

Answer 34

A rate

Question 35

Number of cervical cancer cases in 2012/Number of women at risk in 2012
Is the above example a rate, a ratio or a proportion

Answer 35

A rate