Four studies were done to measure the risk of heart attack among males who were age 60 years at enrollment. Each study subject was followed for the entire follow-up period; there were no drop-outs or loss to follow-up. Details from each of these studies is shown below.

	# of subjects	Time followed	Number of cases
Study 1	100	10 years	10	0.10
Study 2	200	7 years	14	0.07
Study 3	300	5 years	18	0.06
Study 4	400	2 years	8	0.02

Is it correct to conclude that the risk (shown in the last column) of heart attack was greatest in Study 1? Choose the best answer.

a) It is incorrect. For each study, one must divide the number of new cases by the total number of accumulated person*years in order to compare the risks.

b)It is incorrect. The follow-up period is different for each study. One cannot directly compare a 10-year risk with (for example) a 7-year risk.