Question: A prospective cohort study of the association between alcohol consumption and gall bladder disease was designed to follow a group of 400 healthy men over a five-year period. The men were tested for the prevalence of gall bladder disease at the end of each year during the follow-up period. Only new cases of gall bladder disease were recorded at each annual assessment. The results of the study were as follows:

Among the 200 drinkers:
10 subjects were positive for gall bladder disease in year 3.
15 subjects were positive for gall bladder disease in year 5.

Among the 200 nondrinkers:
6 subjects were positive for gall bladder disease in year 2.
4 subjects were positive for gall bladder disease in year 3.

Based on these data, calculate the rate ratio for gall bladder disease in this group. Is there an association between alcohol consumption and gall bladder disease? Explain.