Original ArticleA pragmatic–explanatory continuum indicator summary (PRECIS): a tool to help trial designers
Section snippets
The problem
Randomized trials have traditionally been broadly categorized as either an effectiveness trial or an efficacy trial, although we prefer the terms pragmatic and explanatory. Schwartz and Lellouch describe these two approaches toward clinical trials [1]. These authors coined the terms “pragmatic” to describe trials that help users choose between options for care, and “explanatory” to describe trials that test causal research hypotheses (i.e., that a given intervention causes a particular benefit).
Ten ways in which pragmatic and explanatory trials can differ
Trialists need to make design decisions in 10 domains that determine the extent to which a trial is pragmatic or explanatory. Explanatory randomized trials that seek to answer the question, “Can this intervention work under ideal conditions?” address these 10 domains with a view to maximizing whatever favorable effects an intervention might possess [2]. Table 1 illustrates how an explanatory trial, in its most extreme form, might approach these 10 domains.
Pragmatic randomized trials that seek
Methods
This PRECIS proposal was developed by an international group of interested trialists at two meetings in Toronto (2005 and 2008) and in the time between. The initiative grew from the (PRACTIHC) [7] project, a Canadian and European Union funded initiative to promote pragmatic trials in low- and middle-income countries.
The development of the indicator (which we have named “PRECIS” for “Pragmatic–Explanatory Continuum Indicator Summary”) began with the identification of key domains that distinguish
Participant eligibility criteria
The most extremely pragmatic approach to eligibility would seek only to identify study participants with the condition of interest from as many sources (e.g., institutions) as possible. As one moves toward a more explanatory attitude, additional restrictions will be placed on the study population. These restrictions include the following:
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excluding participants not known/shown to be highly compliant to the interventions under study
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excluding participants not known/shown to be at high risk for the
Examples
To demonstrate the use of the tool, we have applied the instrument to four trials exhibiting varying degrees of pragmatic and explanatory approaches. Table 2 describes how these trials addressed the 10 domains previously described. As we have stated previously, PRECIS is intended to be used at the design stage. We have applied it post hoc to these examples for illustrative purposes only.
The first example uses the trial of self-supervised and directly observed treatment of tuberculosis (DOT) [9]
Comment
The PRECIS tool is an initial attempt to identify and quantify trial characteristics that distinguish between pragmatic and explanatory trials to assist researchers in designing trials. As such, we welcome suggestions for its further development. For example, the tool is applicable to individually randomized trials. It would probably apply to cluster randomized trials as well, but we have not tested it for those designs.
It is not hard to imagine that a judgment call is required to position the
Acknowledgments
The authors are especially indebted to Dr. David L. Sackett for his encouragement and advice during the development of the tool and preparation of this article. We also acknowledge the contributions made by the numerous attendees at the Toronto workshops in 2005 and 2008. The PRACTiHC group was supported by the European Commission's 5th Framework INCO program, contract ICA4-CT-2001-10019. The 2005 Toronto meeting was supported by the Canadian Institutes for Health Research grant number FRN
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This article is being published in both the Canadian Medical Association Journal and the Journal of Clinical Epidemiology.