The qualification period.

For randomized trials that do not require prompt onset of therapy, a pre-admission preparation, called the qualification period, can deal with certain customary difficulties in design, analysis, and ethics. For the patients' baseline state, the qualification period can be used to "wash out" effects of previous treatment, to verify admission criteria, and to identify or stratify suitable prognostic indicators. For treatment, the qualification period can be used to test and adjust therapeutic dosages, to exclude placebo responders, and to confirm early responsiveness to long-term active therapy. For intention-to-treat analyses, the qualification period can allow special stratifications for patients who are therapeutically difficult to regulate or who comply imperfectly. By offering the cited improvements as well as a brief "pilot exposure" for each patient, the qualification period can also enhance the "informed consent" and general ethics of a trial.