Question

consider the following scenario to answer questions 12 through 14. a hypothetical cohort study was undertaken among 1000 college students aged 18 to 24 in the u.s. the purpose of the study was to examine whether daily multivitamin use during college reduces the risk of heart disease later in life. the students were followed for 30 years, and the following data were obtained from the study. in this study, the authors used a measure defined as (75/5000)/(500/15000). what is this measure of association called? (1 point) a prevalence ratio b incidence density ratio (i.e., rate ratio) c relative risk d odds ratio

Explanation:

• Prevalence ratio measures the proportion of existing cases. But here we are dealing with new cases (incidence) over person - years (a rate measure).
• Incidence density ratio (rate ratio) is calculated as \(\frac{\text{Incidence rate in exposed group}}{\text{Incidence rate in un - exposed group}}\). The incidence rate is \(\frac{\text{Number of new cases}}{\text{Person - years of follow - up}}\). For the multivitamin use (exposed) group, the incidence rate is \(\frac{75}{5000}\), and for the non - multivitamin use (un - exposed) group, it is \(\frac{500}{15000}\). The measure \(\frac{75 / 5000}{500 / 15000}\) is a ratio of incidence rates (incidence density ratio).
• Relative risk is the ratio of cumulative incidences (when we have counts of people and follow - up time is not considered in the denominator for each group in the same way as here).
• Odds ratio is used in case - control studies (not a cohort study with person - years of follow - up as here).

Answer:

B. Incidence density ratio (i.e., rate ratio)