Screening and selection process for studies of menstrually-related changes

The screening process of women who volunteered to participate in "studies of the menstrual cycle" is described. It is demonstrated that in order to arrive at a desired number of subjects who meet criteria for premenstrual changes and are in a good physical and mental status, one should recruit an extremely large number of candidates to start with. The yield of each screening procedure is presented. It is clear that fulfillment of inclusion and exclusion criteria can be obtained by a phone interview while important criteria can be clarified only by prospective monitoring of symptoms and personal structured interviews. Methods and procedures that can improve yield and decrease effort in recruitment are suggested.