BACKGROUND Exemplified by a randomised trial on antimanic treatment, this paper addresses the question of whether selection of patients for drug trials may limit the applicability of study results from the randomised patients to a wider population.
METHOD During two-year period, all consecutively admitted patients from a defined catchment area were screened for inclusion criteria concerning age, diagnosis and severity of illness. The subsequently excluded subgroups of patients were compared with the randomised patients by multivariate data analysis.
RESULTS One hundred and sixty-four patients met the inclusion criteria. However, after exclusion for various reasons, only 27 (17%) patients remained for randomisation. The randomised patients and the excluded patients differed substantially.
CONCLUSIONS The generalisability of trial results is limited. Reports of randomised drug trials should carefully describe the screening procedure for inclusion and, when possible, present relevant comparisons-between the randomised patients and the various subgroups of excluded patients.