Epidemiological Measurements Of Morbidity And Mortality Flashcards
WhT are epidemiological measures
Epidemiologic measures represent an application of common mathematical terms to the description of the health of the population
Epidemiologic measures provide information on:
•The frequency of a disease or condition
•Associations between exposures and health outcomes
•Strength of the relationship between an exposure and a health outcome
True or false
True
What must you consider in defining the numerator and denominator
Defining the numerator
•Case definition (condition) — carefully defined in a manner that can be replicated by others
•Frequency—How many cases are there?
•Severity—Some epidemiologic measures employ morbidity as the numerator and others use mortality
•Defining the denominator
•Does the measure make use of the entire population or a subset of the population?
•Some measures use the population at risk
What is the The simplest and most frequently performed quantitative measure in epidemiology and explain it
Count and it is the Refers to the number of cases of a disease or other health phenomenon being studied
- Significant for rare diseases or symptom presentations
- e.g., case of Ebola virus
Ratio is a value obtained by dividing one quantity by another
The most general form has no specified relationship between numerator and denominator
•Proportions, percentages, and rates are also ratio
Give two examples of ratio
Gender ratio
Male divided by female is equal to Male:Female
Example- 950/50 females is equal to 19 males : 1 female
What is proportion and what is it used for
measure that states a count relative to the size of the group.
•A ratio in which the numerator is part of the denominator.
- May be expressed as a percentage
- A percentage is a proportion that has been multiplied by 100
Use-Can demonstrate the magnitude of a health problem relative to size of a group
•Example:
•10 dormitory students develop hepatitis.
•How important is this problem:
•If only 20 students live in the dorm?
•0.50 (50%) are ill.
What is rate and what elements does it contain
a ratio that consists of a numerator and a denominator and in which time forms part of the denominator.
•Contains the following elements:
•disease frequency
•unit size of population
•time period during which an event occurs
What are the measures of disease frequency in epidemiology and state em
The term incidence refers to the occurrence of new disease or mortality within a defined period of observation (e.g., a week, month, year, or other time period) in a specified population.
Prevalence
•The number of existing cases of a disease or health condition in a population at some designated time
Name and explain the types of incidence
Cumulative Incidence
•Describes the rate of development of a disease in a group over a certain time period.
•Contains three elements:
•Numerator = the number of new cases.
•Denominator = the population at risk.
•Time = the period during which the cases occur.
Incidence rate
•An incidence measure used when members of a population or study group are under observation for different lengths of time.
Who are the population at risk
members of the population who are capable of developing the disease or condition being studied
Uses of incidence data
the effects of exposure on health outcomes
•the risks associated with certain exposures; “. . . the probability of someone in that population developing the disease during a specified period, conditional on not dying first from another disease.”
Formula for cumulative incidence is
Cumulative incidence Rate
Cumulative incidence =
Number of new cases
over a time period
Total population at risk during the same time period X multiplier (e.g., 100,000) Number of new cases = 1,085 Population at risk = 37,105 Period =8 years Cumulative Incidence = 1,085 37,105 = 0.02924/8 = 365.5 cases per 100,000 women per year = 0.003655 x 100,000
Formula for incidence rate
- Cumulative incidence rate: number of new cases during the time period divided by total person time observation
- incidence rate:number of new cases during the time period divided by total person years observation
Person- years is equal to the sum of the number of subjects times the total duration of the lengths of observation
True or false
True
Name and explain the types of prevalence with their formulas
Point Prevalence
•All cases of a disease, health condition, or deaths that exist at a particular point in time relative to a specific population from which the cases are derived
Point Prevalence
Point Prevalence =
Number of persons ill
Total number in the group
at point in time
Example:
Total number of smokers in the group = 6,234
Total number in the group 41,837
or 14.9%
= 149.0 per 1,000
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Period Prevalence
•All cases of a disease, health condition, or deaths that exist within a point of time relative to a specific population from which the cases are derived
Number of persons ill over a period of time divided by Average population
Example:
People who have been diagnosed w cancer divided by average population
Prevalence of diarrhea in a children’s camp on July 13 was 33% is an example of what type of prevalence and Prevalence of cancer in women during between July 13 and July 30 period was 33% is another example of what type of prevalence
Point and period prevalence
Uses or prevalence
Provides an indication of the extent of a health problem.
Describing the burden of a health problem in a population.
- Estimating the frequency of an exposure.
- Determining allocation of health resources such as facilities and personnel.
What causes increased or decreased prevalence
Increased prevalence
•Longer duration of the disease
•Prolongation of life of patients without cure
•Increase in new cases (increase in incidence)
•In-migration of cases
•Out-migration of healthy people
•In-migration of susceptible people
•Improved diagnostic facilities (better reporting)
Decreased prevalence •Shorter duration of disease •High case-fatality rate from disease •Decrease in new cases (decrease in incidence) •In-migration of healthy people •Out-migration of cases •Improved cure rate of cases
Prevalence is equal to incidence rate times duration true or false
True
When does prevalence become similar to incidence
If duration of disease is short and incidence is high, prevalence becomes similar to incidence.
If duration of disease is short and incidence is high, prevalence becomes similar to incidence.
•Short duration–cases recover rapidly or are fatal.
•Example: common cold
When does prevalence increases greatly relative to incidence
If duration of disease is long and incidence is low, prevalence increases greatly relative to incidence.
•Example: many chronic diseases
Types of rates
Crude Rates
•Specific Rates
•Adjusted Rates
Where an incidence rate applies to an entire population, it is referred to as a crude rate.
True or false
True
Formula for crude death rate and crude birth rate
Number of deaths in a given year divided by reference population during midpoint of the year multiplied by a reasonable multiplier that’ll give a whole number
Number of live births within a given period Divided by Population size at the middle of that period times a reasonable Multiplier
What ar ethe implications of crude rate
Use crude rates with caution when comparing disease frequencies between populations
- Observed differences in crude rates may be the result of systematic factors (e.g., sex or age distributions) within the population rather than true variation in rates
- To correct for systematic population factors that influence crude rates, Specific and Adjusted rates may be constructed
What’s re specific rates and give three examples
Rates
•Specific rates refer to a particular subgroup of the population defined in terms of race, age, sex, or they may refer to a entire population, but be specific for some single cause of death or illness.
Examples •Cause-Specific Rates •Age-Specific Rates •Sex-Specific Rates •Proportional Mortality Ratio
What is case specific rate and an example and a formula
The cause-specific rate is a measure that refers to mortality (or frequency of a given disease) divided by the population size at the midpoint of a time period times a multiplier
Example
•Cause-specific mortality rate – rate associated with a specific cause of death
Cause-Specific Rate =
Mortality (or frequency of a given disease)
Population size at midpoint of time peri
What is age specific rate and the formula
An age-specific rate refers the frequency of a disease (or health condition) in a particular age stratum divided by the total number of persons within that age stratum during a time period.
Age-Specific Rate =
Number of deaths (or disease) among those aged 15–24 years
Number of persons among aged 15–24 years during time period
What is sex specific rate and the formula
sex-specific rate refers to the frequency of a disease in a gender group divided by the total number of persons within that gender group during a time period times a multiplier.
Number of deaths among males = 1,207,675
•Number of deaths among females = 1,240,342
•Estimated number of males in the population as of July 1, 2005 = 145,999,746
•Estimated number of females in the population as of July 1, 2005 = 150,410,658
- Calculate the sex-specific rate for males per 100,000
- = 1,207,675/145,999,746 × 100,000
- = 827.2 per 100,000
- Calculate the sex-specific rate for females per 100,000
- = 1,240,342/150,410,658 × 100,000
- = 824.6 per 100,000.
What is proportion mortality rate and the formula
The proportional mortality ratio (PMR) is the number of deaths within a population due to a specific disease or cause divided by the total number of deaths in the population.
•Indicates relative importance of a specific cause of death; not a measure of the risk of dying of a particular cause
PMR (%) =
Mortality due to a specific cause during a time period divided by
Mortality due to all causes during the same time period
X 100
What are adjusted or standardized rates
Summary measures of the rate of morbidity and mortality in a population in which statistical procedures have been applied to remove the effect of differences in composition of various populations.
What’s re the types of adjusted or standardized rates and explain
Direct Method
•Direct method may be used if age-specific death rates in a population to be standardized are known and a suitable standard population is available
•Each age-specific death rate in the population to be standardized is multiplied by the number of persons in each age group of the standard population
•The result is the expected number of death in each age group, which is then summed across all age groups to determine the number of expected deaths
Indirect method may be used if age-specific death rates of the population for standardization are unknown or unstable, for example, because the rates to be standardized are based on a small population
•The number of persons in each age group in the population to be standardized is multiplied by the age-specific death rate of the standard population
•The result is the expected number of death in each age group, which is then summed across all age groups to determine the number of expected deaths
•
The standardized mortality ratio (SMR) can be used to evaluate the results of the indirect method. What is the formula?
Total Observed deaths divided by
Total Expected deaths times 100
If the observed and expected numbers are the same, the SMR would be ? And what does it indicate
1.0 (or 100%), indicating that observed mortality is not unusual.
If the SMR is less than 1.0 (<100%)?
- If the SMR is greater than 1.0 (>100%) it means?
- E.g. An SMR of 2.0 (200%) means that the death rate in the study population is two times greater than expected true or false
- it means the death rate is in the study population is less than expected
- it means the death rate is in the study population is more than expected
True
Calculate SMR and crude death rate :SMR is (502/987.9) X 100 = (0.51) 51%. This means what for the death rate?
•The
death rate in the study population of interest is 0.51 (51%) times less than expected
What is a hazard, what is a risk
Hazard refers to the potential to cause harm
Hence risk is a statement of probability that an event (death, disease etc) will occur.
Risk
•Thus, risk is a statement of probability that an event (death, disease etc) will occur
•
Risk ranges from 0 to 1
- Risk can generally be estimated as the incidence of an event (death, disease etc)
- Therefore rates are an indicator of risk and other measures of risk are Relative risk (risk ratio/rate ratio)
- Attributable risk (Absolute risk difference)
True or false
True
A two by two table is useful for doing what?
useful tool for viewing study results and calculating effect measures for comparing groups
•This can be done with relative or absolute effect measures
What is relative risk used for and interpretation of relative risk
Relative risk is used to compare the incidence of a disease or condition between a group with a particular attribute or exposure to one without.
Relative risk is a measure of the strength of an association between an exposure or attribute and a disease.
If the relative risk is 1 then?
- If it is greater than 1,
- If less than 1,
then the incidence in the two groups is the same.
- then the attribute or exposure is associated with an increased incidence of the disease,
- with a decreased incidence of the disease
Example of relative risk of getting lung cancer from smoking :is (number of smokers or exposed group with lung cancer divided by number of smokers with no lung cancer plus number of smokers with lung cancer ) all divided by (number of non smokers or non exposed group divided by non smokers w lung cancer divided by non smokers with no lung cancer plus non smokers with lung cancer)
True or false
True
What is a risk factor and when an exposure is indentified as a risk factor for a disease what does it mean
Factors which may be causes of the disease and which, if removed or modified, would prevent the disease occurring
- When an exposure or attribute is identified as a risk factor for a disease, it simply means that:
- It is associated with an increased probability (risk) of the disease occurring.
- It does not mean that the factor is a cause of the disease
•For example, over 200 risk factors identified for coronary heart disease (siestas, snoring, English as a mother tongue and not eating mackerel etc)
What is attributable risk
Attributable risk is used to provide an assessment of how much of a disease is ‘due to’ an exposure and so we can assess how much might be prevented if an exposure is removed
•Simple the difference in frequency of a disease between two groups (exposed vs. non-exposed),
State the types of atributable risks and explain
Attributable risk (exposed) •Refers to the rate of a disease or condition among exposed individuals that can be attributed to the exposure
•Attributable risk (exposed) = Incidence among the exposed − incidence among non-exposed
Look on slide for formula example
Attributable risk (population) is the rate of a disease or condition among the total population which can be attributed to the exposure.
•Attributable risk (population) = Incidence among total population − incidence among non-exposed
Name three interpretations of attributable risk interpretations
That the exposure (in this case smoking) “causes” the disease (lung cancer)
2.That other “causes” of the disease are equally distributed among the exposed (smokers) and unexposed (non-smokers)
•#That the rate of the disease in the exposed group will return to that in the non-exposed if the exposure is removed
Name the public health relevance of relative risk and attributable risk
Relative risk and attributable risk provide two very different types of information
- Relative risk is a measure of the strength of the association between an exposure and a disease.
- It is used to help assess whether or not an exposure is one of the ‘causes’ of a disease.
The attributable risk (population) provides an estimate of the benefit that might be expected within the total population if exposure to a given factor is removed
•Thus attributable risk (population) is helpful when guiding preventive health measures aimed at improving the health of a population
The strength of the association and whether or not there is a ‘dose response’ relationship between the occurrence of the disease and the exposure are two factors often used to assess if the exposure is likely to be causal. E.g smoking and lung cancer
True or false
True
- The potential benefits of removing different exposures can be assessed using attributable risk
- This can be useful in helping to decide which exposures it is worth trying to prevent.
True or false
True
Smoking: exposed 80/100 divided by 20/100 non-exposed for relative risk and 80/100 -20/100 for attributable risk interpretation
Relative risk: 80/100 ÷ 20/100 = 4
i.e. those exposed to smoking have 4 times the risk of developing lung cancer as those not exposed to smoking
Attributable risk: 80% - 20% = 60%
i.e. for every 100 people exposed to smoking there will be 60 extra cases of lung cancer.
Difference between crude date and specific rates
Crude rate is the rate in which the denominator includes the total population. Specific rate stands for the rate that measures morbidity or mortality for particular population or diseases.
