I want to do an association between obesity and driving in a case-control study. If my case was drivers, what should the control be? Should it also be a driver or other job?
There are quite a few factors involved in obesity that might make this particular type of study questionable. The first is simply the correlation between sedentary lifestyles and obesity. Less active people tend to be more obese. The difference between shorter drives and long hauls is not just the amount of sitting time, but also the more likely activity frequency getting in and out of a vehicle, particularly when assisting in package delivery services. The driving distances alone are not likely a good predictive correlation.