A cohort study of coffee drinking and anxiety was conducted at a university campus. There were a total of 30,000 freshmen who participated. 10,000 were coffee drinkers and 20,000 were not. Of the coffee drinkers, 500 developed anxiety during the 4 year follow-up period. Of the non-coffee drinkers, 200 developed anxiety during the same time period. Assume that no one in the population died or was lost during the follow-up period. Calculate the population risk difference using the given data. The numeric value of the population risk difference is...
a. 1.3 (per 100)
b. 2.7 (per 100)
c. 3.3 (per 100)
d. None of the above