Effect of study criteria on recruitment and generalizability of the results.

OBJECTIVE: Clinical trials are indispensable to drug approval process. This research examined the effect of a specific study criteria on recruitment and generalizability of the results.
METHODS: The following were reviewed: (a) the usual inclusion and exclusion criteria for the antipsychotic trials performed at the Institute; (b) epidemiologic data, to determine the effect of study criteria on the target population; and (c) the recruitment procedures/strategies used to identify potential candidates. A survey was conducted to determine the percentage of schizophrenic patients in a conventional outpatient psychiatric clinic conforming to the usual enrollment criteria for antipsychotic trials.
RESULTS: Intensive recruitment efforts in a general population of 3.6 million would have been expected to yield only 632 eligible subjects out of 36,000 suffering from schizophrenia. Out of 632, only 50 contacted the research site after an intensive recruitment effort. From those 50, 30 were excluded during a telephone interview. Of the 20 remaining, 6 were excluded for a variety of reasons during a face-to-face interview. Thus, only 14 subjects out of a population of 3.6 million met the study criteria.
CONCLUSIONS: These results emphasize the rarified nature of patients-volunteers who enter a clinical trial. Inclusion and exclusion study criteria can severely restrict the number of eligible subjects, dictate recruitment strategies, and in turn affect generalizability of the results.