In a case-control study, which of the following is true?
a. The proportion of cases with the exposure is compared with the proportion of controls with the exposure
b. Disease rates are compared for people with the factor of interest and for people without the factor of interest
c. The investigator may choose to have multiple comparison groups
d. Recall bias is a potential problem
e. a, c, and d
Answer: e. a, c, and d