Epidemiology Ucc Flashcards

Question

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. ### 1. Which of the following scenarios is best measured by cumulative incidence rather than incidence rate? 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% ** ### 3. In an observational study, researchers find an incidence rate of 25 cases per 1,000 person-years for a specific condition. Which of the following statements is correct regarding the use of the incidence rate? 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. ### 5. If a researcher is studying the occurrence of a disease with gradual onset in a population over a long period, which measure is most likely to be used, and why? 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 1

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: ### Cumulative Incidence - **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: \[ \frac{50}{1000} = 0.05 \text{ or } 5\% \] ### Incidence Rate - **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: \[ \frac{50}{1000 \text{ person-years}} = 0.05 \text{ per person-year} \] ### Key Differences 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. ### Example Scenario 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: ### **1. Incidence Rate (Person-Time Rate/Incidence Density):** - **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. ### **2. Cumulative Incidence (Incidence Proportion/Risk):** - **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. ### **Key Differences:** 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. ### **Example Scenario:** - **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. ### Think of it Like This: 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. ### 1. **Cumulative Incidence** (Risk Over Time) - **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. ### 2. **Incidence Rate** (Speed of New Cases) - **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. ### **The Main Difference Related to Risk and Follow-Up**: - **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. ### Summary: - **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. ### 1. Which of the following scenarios is best measured by cumulative incidence rather than incidence rate? 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. ### 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% **Answer:** B. 5% ### 3. In an observational study, researchers find an incidence rate of 25 cases per 1,000 person-years for a specific condition. Which of the following statements is correct regarding the use of the incidence rate? 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. ### 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. **Answer:** B. It is used to estimate the risk of developing a disease over a defined period in a closed cohort. ### 5. If a researcher is studying the occurrence of a disease with gradual onset in a population over a long period, which measure is most likely to be used, and why? 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!

Answer 2

It is suitable for communicating health information to decision-makers

Answer 3

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

Answer 4

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: ### **1. Proportion vs. Percentage:** - **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%. ### **2. Incidence Proportion (Cumulative Incidence):** - **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: \[ \text{Incidence Proportion} = \frac{50}{1000} = 0.05 \text{ (or 5% when expressed as a percentage)} \] ### **3. Why Express in 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." ### **4. Risk and Incidence Proportion:** - **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.

Answer 5

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

Answer 6

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.

Answer 7

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

Answer 8

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% 5. 3/7x100=

Answer 9

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.

Epidemiology Ucc Flashcards

(35 cards)