If you want to know which of two or more healthcare interventions is most effective, the randomised controlled trial is the design of choice. Randomisation, however, does not itself promote the applicability of the results to situations other than the one in which the trial was done.  A tool published in 2009, PRECIS -PRagmatic Explanatory Continuum Indicator Summaries ( – aimed to help trialists design trials that produced results matched to the aim of the trial, be that supporting clinical decision-making, or increasing knowledge of how an intervention works. Though generally positive, groups evaluating the tool have also found weaknesses, mainly that its inter-rater reliability is not clear, that it needs a scoring system and that some new domains might be needed. 

The PRECIS-2 will improve and validate a new version of PRECIS through three phases. Phase 1: brainstorming and a 2-round Delphi survey of authors who cited PRECIS, followed by user-testing of candidates for PRECIS-2. Phase 2 evaluated the validity and reliability of the most promising PRECIS-2 candidate using experienced trialists and methodologists and a selection of protocols. Phase 3 aimed to use PRECIS-2 to compare the internal validity and effect estimates a set of matched explanatory and pragmatic trials.

PRECIS-2 is led by Shaun Treweek at the University of Aberdeen and Merrick Zwarenstein at Western University, Canada and is ongoing.  It is also the basis of Kirsty Loudon’s PhD work, which is due for submission in the first half of 2015.

The protocol for the PRECIS-2 study is available at  Further details are available at


Shaun Treweek;