Some adaptive strategies for inadequate sample acquisition in veterans administration cooperative clinical trials.

A major concern of any clinical trial is being able to recruit sufficient patients of the proper type so that reliable answers can be obtained for the hypotheses being tested. This article considers patient recruitment in seven VA cooperative studies and the adaptive strategies used for inadequate sample acquisition. These strategies are: (1) the re-evaluation of the required sample size; (2) the addition of new hospitals; (3) the replacement of poor recruiting hospitals; (4) the extension of the patient intake period; and (5) the modification of the patient exclusion-inclusion criteria. When there is no expectation of achieving the required sample size in a reasonable time, the study is terminated. Although each of the five strategies will increase the likelihood of successfully completing a study should a recruitment problem occur, preventing these problems from occurring should be a major concern during the planning of a study.