A cohort study was conducted, enrolling 15,000 participants without a history of stroke. During the 15-year follow-up period, 440 cases of stroke occurred, of which 284 were classified as eating a poor diet (did not reach the recommended daily fruit and vegetable intake). Those reporting a poor diet contributed a total 126,550 person-years during the completed study. Those who reported a good diet that met the recommended daily fruit and vegetable intake contributed a total 96,422 person-years of follow-up.
Calculate the relative risk of stroke in those exposed to the study factor.
Report and interpret the meaning of the measure you calculate.
Physical activity levels of participants were recorded during the study. The investigators analysed the data further to understand whether “low” physical activity (i.e. not meeting the recommended levels of physical activity) was a confounder of the association between a poor diet and incident stroke. They calculated the following values:
The RR of stroke among those with a poor diet for those reporting low physical activity. RR = 1.05
The RR of stroke among those with a poor diet for those reporting they met the recommended levels of physical activity. RR = 1.02 Is “low” physical activity a confounder of the association between a poor diet and incident stroke?
Give reasons for your answer.