Reasons why patients do or do not participate in clinical trials; a systematic review of the literature

Objective. To assess the factors that may influence a patient's consent to participate in a clinical trial. Design. Systematic literature survey. Method. Studies on the characteristics of patients, trials, the physicians requesting informed consent and the informed consent procedures were looked for in Medline, Embase, and Cinahl. Articles published in English, German, Dutch or French in the period 1980-2002 and originating in Europe, the United States, Canada, New Zealand or Australia were included. Studies on non-adults, healthy experimental subjects or less than 30 patients were excluded. Results. Thirty suitable studies were retrieved. Factors that may affect the granting of consent to participate in a clinical trial included: uncertainty of the patient, randomisation and the use of a placebo, the relationship between the person asking for informed consent and the patient, and the dissemination of information during the informed consent procedure. Since these factors are often interrelated, no single factor could be identified as decisive for participation in a clinical trial; they can influence the decision of the patient to participate in a trial in either a positive or a negative direction. Conclusion. Optimalization of the information concerning informed consent. the way the information is provided and the attitude of the person requesting informed consent are important and sometimes decisive factors that may determine the participation process.