A five-year prospective cohort study has just been completed. The study was designed to assess the association between supplemental vitamin A exposure and mortality and morbidity from the measles. The RR for incidence of the measles was 0. 85 and the RR for measles mortality was 0.7. Which statement is correct? a. A cohort study is not an appropriate study design in this case because the association between one exposure and two different outcomes is being considered.
b. One of the problems that this study may have faced is individuals lost to follow-up during the five-year period.
c. A cohort study is not a good design to study this association because measles is a very common disease.