In cohort studies of the role of a suspected factor in the etiology of a disease, it is essential that: The exposed and non-exposed groups under study be as similar as possible with regard to possible confounding factors.
The Review Questions answers do not address (why nots)...So why is the answer not: There should be equal numbers of persons in both study groups???
Equal number of perswon in each group does not ensure that the groups are similar. When we are measuring effect of a treatment, we need to ensure that the effect of all the factors which are not being measured ...
The solution examines Cohort Studies of the role of a suspected factor in the etiology of a disease.