An advantage of a prospective study over a retrospective study is
A. prospective studies are generally less expensive because the researcher has some control over the participants.
B. prospective studies have fewer problems in data inaccuracies and missing data.
C. prospective studies need fewer participants in the study in order to obtain the same level of precision.
D. a prospective study is a controlled study whereas a retrospective study is an observational study.
E. all of the above answers are correct.