Question

Research suggests that there is a dose response relationship between physical activity levels and mental health. Suppose that the table shown below was developed using data from a 10-year cohort study. Participants were categorized based on their physical activity levels and followed over time to see if they developed a mental health disorder. The referent group were those who did not exercise.

Exposure Status	Cases of Mental Health Disorders	Person Years of Observation
No exercise	50	20,000
Occasional exercise	20	18,000
Frequent exercise	7	13,000

1. Calculate the incidence rate of mental health disorders per 1,000 person-years of observation among the referent group (i.e. the unexposed). (2 points)

1. 0.54
2. 1.0
3. 1.11
4. 2.5

Answer 1

D. 2.5

Incidence rate of mental health disorders per 1000 person years of observation among the referent group(those who did not exercise which is 50)) .

Incidence rate per 1,000 = No. of new cases of a disease occuring in the population during a specified period of time / No. of persons who are at risk of developing the disease during that period of time. * 1,000   

= 50 / 20000 * 1000

= 2.5

Therefore, incidence rate of mental health disorders per 1000 person years of observation among the referent group is 2.5