Participant recruitment for an anorexia nervosa treatment study.

Objective: To investigate the nature of differing recruitment rates for clinical treatment trials for anorexia nervosa and bulimia nervosa.

Methods: Recruitment rates from a study recruiting women partially recovered from anorexia nervosa were compared with the rates from two studies conducted at the same sites recruiting women with bulimia nervosa.

Results: At all sites in the anorexia study, the total number of contacts per month rose steadily over the first 2 years of the recruitment phase then decreased to near zero with the number of participants randomized to the study practically evaporating. In contrast, the bulimia studies screened a larger group of contacts and met monthly randomization goals in the time allotted for recruitment. Participants eligible for a study but with a barrier to participation occurred at a much higher rate in the anorexia study than in the bulimia studies.

Discussion: These results reveal a difficulty in planning recruitment from a small population such as partially recovered anorexics. A small population's total pool size diminishes faster than it is replenished, suggesting that future studies of anorexia nervosa may recruit more successfully from many sites in a short period rather than at a few sites over a long period.