A cohort study of coffee drinking and anxiety was conducted among 30,000 freshmen. 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 study died or was lost during the follow-up period.
Calculate the risk difference using the given data. The numeric value of the risk difference is:
- 6%
- 4%
- 5%
- None of the above