Review

Making trials matter: pragmatic and explanatory trials and the problem of applicability

Shaun Treweek^1,2 and Merrick Zwarenstein^3,4,5

¹  Division of Clinical and Population Sciences and Education, University of Dundee, Dundee, UK

²  Norwegian Knowledge Centre for the Health Services, Oslo, Norway

³  Centre for Health Services Sciences, Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada

⁴  Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada

⁵  Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada

author email corresponding author email

Trials 2009, 10:37doi:10.1186/1745-6215-10-37

Published:	3 June 2009

Abstract

Randomised controlled trials are the best research design for decisions about the effect of different interventions but randomisation does not, of itself, promote the applicability of a trial's results to situations other than the precise one in which the trial was done. While methodologists and trialists have rightly paid great attention to internal validity, much less has been given to applicability.

This narrative review is aimed at those planning to conduct trials, and those aiming to use the information in them. It is intended to help the former group make their trials more widely useful and to help the latter group make more informed decisions about the wider use of existing trials. We review the differences between the design of most randomised trials (which have an explanatory attitude) and the design of trials more able to inform decision making (which have a pragmatic attitude) and discuss approaches used to assert applicability of trial results.

If we want evidence from trials to be used in clinical practice and policy, trialists should make every effort to make their trial widely applicable, which means that more trials should be pragmatic in attitude.