Question

a hypothetical cohort study was undertaken among 600 adhd - free children in south carolina. the purpose of the study was to examine the effects of increased screen time during childhood on the subsequent diagnosis of adhd by young adulthood. the childrens screen time was assessed by a questionnaire, and the children were followed for 10 years. the following data were obtained from the study.
interpret in words the measure of association calculated in question 3. (2 points)
a the risk of adhd among children exposed to at least 4 hours per day of screen time is 1.27 times the risk of adhd among children exposed to less than 4 hours per day of screen time.
b the odds of adhd among children exposed to at least 4 hours per day of screen time is more than 1.27 times the odds of adhd among children exposed to less than 4 hours per day of screen time.
c the prevalence ratio of adhd among children exposed to at least 4 hours per day of screen time is more than 1.27 times the prevalence ratio of adhd among children exposed to less than 4 hours per day of screen time.
d the relative risk of at least 4 hours of screen time among children exposed to adhd is 1.27 times the risk of at least 4 hours of screen time among children not exposed to adhd.

Explanation:

This is a cohort study. In a cohort study, the measure of association is often the relative risk (risk ratio). The formula for relative risk in a cohort study is \(RR=\frac{\text{Risk in exposed group}}{\text{Risk in un - exposed group}}\). The risk in the exposed group (screen time ≥ 4 hours) is \(\frac{125}{260}\), and the risk in the un - exposed group (screen time < 4 hours) is \(\frac{175}{340}\).

The relative risk (RR) interpretation is about comparing the risk of the outcome (ADHD) between the exposed and un - exposed groups.

Option A: It correctly interprets the relative risk (risk ratio) concept. The risk (probability of getting ADHD) in the exposed group (screen time ≥ 4 hours) compared to the un - exposed group (screen time < 4 hours).

Option B: Incorrect because it refers to odds (used in case - control studies, not cohort studies for the primary measure of association).

Option C: Incorrect as it mentions prevalence ratio (prevalence is a cross - sectional measure, not for cohort studies which are about incidence - based risk).

Option D: Incorrect as it has the exposure and outcome reversed in the relative risk interpretation.

Answer:

A. The risk of ADHD among children exposed to at least 4 hours per day of screen time is 1.27 times the risk of ADHD among children exposed to less than 4 hours per day of screen time.