Study control, violators, inclusion criteria and defining explanatory and pragmatic trials

Stat Med. 2002 May 30;21(10):1365-76. doi: 10.1002/sim.1120.


Important differences between explanatory and pragmatic studies were originally argued by Schwartz and Lellouch. Three important differences between the two types of study involve study control, study violators and inclusion criteria. It was originally argued that explanatory studies are highly controlled, and pragmatic studies may be looser and more like 'real life'. It was argued that an explanatory study should only analyse those receiving treatment, and a pragmatic study would analyse all randomized patients. Explanatory trials are said to use homogeneous groups, and pragmatic studies have less selection (better generalizability). Some suggestions are put forward to update the original distinctions between these two attitudes for future study design. Poor study control is undesirable (but might be necessary) and should not be welcomed as pragmatic. The intention-to-treat strategy is now considered as standard for nearly all trials. Homogeneity is a red herring for studies in humans. Inclusion criteria should be minimized and they should not be used to justify claims of representativeness. Routine criticism of randomized controlled trials for being unrepresentative is unwarranted. We should accept that most trials in humans are 'explanatory'. The division line should be moved, so that pragmatic studies are in the domain of non-therapeutics and complex treatments.

MeSH terms

  • Humans
  • Patient Dropouts
  • Patient Selection
  • Randomized Controlled Trials as Topic / methods*
  • Research Design / standards*