Randomised controlled trials are widely accepted as the most
reliable method of determining effectiveness, but most trials
have evaluated the effects of a single intervention such as a
drug. Recognition is increasing that other, non-pharmacological
interventions should also be rigorously evaluated.1–3 This paper
examines the design and execution of research required to
address the additional problems resulting from evaluation of
complex interventions—that is, those “made up of various
interconnecting parts.”4 The issues dealt with are discussed in
a longer Medical Research Council paper
(www.mrc.ac.uk/complex_packages.html). We focus on randomised
trials but believe that this approach could be adapted to other
designs when they are more appropriate. - Complex interventions
are those that include several components - The evaluation of
complex interventions is difficult because of problems of
developing, identifying, documenting, and reproducing the
intervention - A phased approach to the development and evalua