Background: Clinical trials have traditionally been broadly categorized as either explanatory/efficacy trials or pragmatic/effectiveness trials. Explanatory trials are aimed at determining if an intervention can work under ideal circumstances whereas pragmatic trials attempt to show if an intervention will work under routine conditions in the usual settings. The difference in the level of pragmatism could explain part of systematic reviews' heterogeneity. Very few trials are purely explanatory or pragmatic. Instead, there is a continuous, rather than dichotomous description of the explanatory-pragmatic distinction. A "Pragmatic-Explanatory Continuum Indicator Summary" (PRECIS) was developed by a working party of an international consortium who is promoting pragmatic clinical trials in health care in low and middle-income countries (PraCTIHC)1. We will explore how useful this indicator can be to explain heterogeneity of a systematic review of clinical trials.
Objectives: To assess the utility of PRECIS to explain the heterogeneity of a systematic review of clinical trials.
Methods: PRECIS involves eight key dimensions and 5-level Likert scales for each of these dimensions: 1. The eligibility criteria for study participants. 2. The flexibility with which the intervention is applied. 3. The degree of practitioner expertise in applying and monitoring the intervention. 4. The intensity of follow-up of trial participants. 5. The duration of follow-up of trial participants. 6. The intensity of measuring participants' compliance with the experimental intervention, and whether compliance-improving strategies are employed. 7. The intensity of measuring collaborators' adherence to the study protocol, and whether adherence-improving strategies are employed. 8. The specification and scope of the primary analysis. We selected a Cochrane review with significant heterogeneity between studies2. Two researchers will independently apply the PRECIS and assign a summary value to each of the 51 included trials. Disagreements will be solved by a third researcher. Next, we will rerun the analysis of the systematic review incorporating pragmatism as source of heterogeneity by subgroup analysis and meta-regression.
Results and Conclusions: Will be presented at the XV Cochrane Colloquium.

References
1. http://www.practihc.org/
2. Duley L, Henderson-Smart DJ, Knight M, King JF. Antiplatelet agents for preventing pre-eclampsia and its complications. Cochrane Database of Systematic Reviews 2003, Issue 4. Art. No.: CD004659. DOI: 10.1002/14651858.CD004659