Pragmatic clinical trials
Introduction
Clinical trials can be designed to be either pragmatic or explanatory.1 Pragmatic trials are designed to find out about how effective a treatment actually is in routine, everyday practice. Explanatory trials are designed to find out whether a treatment has any efficacy (usually compared with placebo) under ideal, experimental conditions. Both have a place in our repertoire of research methods. In this paper I will describe the key steps in undertaking a pragmatic trial, and describe some differences from an explanatory trial. My focus will be on the parallel-arm design, although the principles can be applied to other types of study. I will explore some of the strengths and weaknesses of pragmatic trials. I will then make some comparisons between archetypal pragmatic and explanatory trials, while acknowledging that some trials have hybrid designs. Finally I will make a case for the relevance of pragmatic trials in the clinical evaluation of complementary therapies.
Section snippets
Appropriate research question
The study design should match the clearly defined research question: if you are interested in evaluating the benefits of a therapy in everyday practice, then you need to use a normal clinical setting and a pragmatic design. Pragmatic trials answer questions about the overall effectiveness of an intervention, and cannot study the contributions of its different components. You would use a pragmatic trial to test an overall ‘package’ of care, including the contribution of the therapeutic
Limitations
The pragmatic trial design cannot be used to determine precisely what components within the treatment process might have caused any benefits, since it is a package of care that is being evaluated. For example, acupuncture is not being tested against a sham or “placebo” intervention, so pragmatic trials will not help isolate the effect of the needling per se. Therefore, the extent that the therapeutic relationship contributes to any overall benefit remains unknown after a pragmatic trial. Using
Comparing pragmatic and explanatory designs
Some features of explanatory and pragmatic trials can be presented archetypically as polar opposites (see Table 1). However, many randomised controlled trials lie somewhere along the spectrum between these two designs. For example, if a pragmatic trial has a more tightly specified treatment protocol than allowing practitioners a free hand to treat normally, then the design is no longer fully pragmatic. Nevertheless Table 1 is intended to highlight the key differences that inform the two types
Conclusion
Both explanatory and pragmatic trials have an important place in the evaluation of health care interventions, but they answer different research questions. Pragmatic trials are useful in answering questions about how effective a therapy is when compared to some standard or accepted treatment. They also overcome some specific difficulties that can be encountered with explanatory trials of complementary therapies, for example when evaluating complex packages of care. Pragmatic trial results can
Acknowledgements
Acknowledgements are due to Adrian White, Sylvia Shroer and Elaine Weatherley-Jones who all made useful suggestions that helped in the editing of this article.
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