A prospective, randomized study of oral contraceptives: the effect of study design on reported rates of symptoms

A study was undertaken to assess the effects of the study design (frequency and method of inquiry about the side effects) on the reporting of oral contraceptive (OC)-associated side effects. The study found that the one-contact-per-cycle schedule yielded consistently lower rates of side effects than the two-contact-per-cycle schedule. Also, asking subjects about the occurrence of specific symptoms led to the reporting of higher rates of side effects than those obtained by general inquiry. The study suggests that differences in the reported rates of side effects may be due in part to the manner in which the data were collected.