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Measures
Question | Answer |
---|---|
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 |