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Measures

What does the (person-time) incidence rate (or incidence density) measure? The disease occurrence per unit time
What does cumulative incidence (incidence proportion) measure? The proportion of study subjects who experience the outcome of interest at any time during the follow-up period
Is the cumulative incidence dimensionless? Yes, but it is necessary to specify the time period over which it is being measured.
Is the incidence rate dimensionless? No, it is a rate per unit time and has the reciprocal of time as its dimension.
When is the cumulative incidence approximately equal to the product of the incidence rate times the follow-up period? When the outcome of interest is rare over the follow-up period
What does the incidence odds measure? Ratio of the number of subjects who experience the outcome to the number of subjects who do not experience the outcome
Is the incidence odds dimensionless? Yes, but it is necessary to specify the time period over which it is being measured.
When is the incidence odds approximately equal to the cumulative incidence? When the outcome of interest is rare over the follow-up period
How are the incidence rate, cumulative incidence, and incidence odds different? Whether their denominators represent person-time at risk, persons at risk, or survivors.
How are the incidence rate, cumulative incidence, and incidence odds similar? They all involve the same numerator: the number of events (deaths)
What does the rate ratio (incidence density ratio) measure? Ratio of the incidence rate in the exposed group to that in the non-exposed group
What does the risk ratio (cumulative incidence ratio) measure? Ratio of the cumulative incidence in the exposed group to that in the non-exposed group
When is the risk ratio approximately equal to the rate ratio? When the outcome of interest is rare over the follow-up period
What does the (incidence) odds ratio measure? Ratio of the incidence odds in the exposed group to that in the non-exposed group
When is the incidence odds ratio approximately equal to the incidence rate ratio? When the outcome of interest is rare over the follow-up period
Which effect measures involves the ratio of a measure of disease occurrence in the exposed group to that in the non-exposed group? All of them: Rate ratio, risk ratio, and odds ratio
How are the rate ratio, risk ratio, and odds ratio similar? They all involve the same numerator: the number of events (deaths)
How are the rate ratio, risk ratio, and odds ratio different? Whether their denominators are based on person-time, persons, or survivors
When are the rate ratio, risk ratio, and odds ratio all approximately equal? When the disease is rare during the follow-up period (e.g., a cumulative incidence of less than 10%)
What are the rate ratio, risk ratio, and odds ratio all collectively called? Relative risk
What does relative risk refer to? A generic term that refers to rate ratio, risk ratio, and/or odds ratio
Which measure of effect is sometimes regarded as the primary effect measure on theoretical grounds? Rate ratio
Which measure of effect is easier to conceptualize, especially by non-epidemiologists? Risk ratio
In a ca/co study, when selecting controls from among survivors, what do the controls estimate? Exposure odds (b/d) of the survivors
In a ca/co study, when selecting controls from among survivors, what does the odds ratio obtained estimate? Odds ratio in the base population
When is the odds ratio approximately equal to the risk ratio? When the disease is rare
In a ca/co study, when selecting controls from the entire base population (those at risk at the beginning of follow-up), what do the controls estimate? Exposure odds in the base population of persons at risk at the start of follow-up
In a ca/co study, when selecting controls from the entire base population, what does the odds ratio obtained estimate? Risk ratio in the base population
Which methods are used to select controls from among survivors? Nested case-control study
Which methods are used to select controls from the entire base population (those at risk at the beginning of follow-up)? Case-cohort study; case-base sampling
Which methods are used to select controls longitudinally throughout the course of the study? Risk-set sampling; density sampling; sampling from the study-base
In a ca/co study, when selecting controls longitudinally throughout the course of the study, what do the controls estimate? Exposure odds in the study base (i.e., the person-time at risk)
In a ca/co study, when selecting controls longitudinally throughout the course of the study, what does the odds ratio obtained estimate? Rate ratio in the study base
Created by: AlneciaPHS