Explanatory and pragmatic clinical trials: a primer and application to a recent asthma trial.

Most clinical trials assessing the role of a specific intervention attempt to answer an explanatory question: under ideal circumstances of risk and responsiveness, can the expert care of individual with a particular condition reduce their risks of a relevant but restricted set of outcomes? Such explanatory trials (also called efficacy trials) are of direct relevance to expert clinicians and their highly compliant patients. Another question, potentially of broader clinical or health care policy relevance is: Does this treatment improve patient-important outcomes when applied by typical clinicians to typical patients? Answering this latter question is the goal of pragmatic trial, also labeled by some as "management" or "effectiveness" trial. The methodological and organizational differences between explanatory and pragmatic trials include, among others, patients eligibility (restricted to highly responsive and compliant patients in explanatory trials vs. everyone with condition of interest in pragmatic trials), experimental and comparator intervention (blinded and inflexible with strict instructions vs. flexible with cross-over permitted and no blinding), types of practitioners (only those with documented high expertise vs. all who usually provide given mode of care), and outcome measurement (often limited to biologic effects vs. broad overall health effects sometimes based on administrative data bases on mortality and utilization). Those aspects of study design and conduct and their role in determining a place of an intervention in clinical practice are reviewed in this paper.