Background: Systematic reviews of effectiveness aim to collate the evidence relating to questions that specify the population(s), intervention, comparator and outcome(s). Where trials are common, narrow review scopes achieve this aim well. Where trials are sparse a broader scope may be required to identify trials at all; yet reviews with a broad scope need careful structuring if they are to describe meaningfully both the evidence available and the gaps in our knowledge about effectiveness.

Objectives: To develop a matrix that will expose knowledge and knowledge gaps in an area where trials are expected to be sparse: consumer involvement in collective healthcare decision making1.

Methods: We developed a matrix based on an earlier framework analysis of consumer involvement informed by theoretical, empirical and policy literature2. The matrix distinguished methods of promoting and facilitating consumer involvement in policy, healthcare research, clinical practice guidelines and patient information material. We searched eight different databases for randomized trials, non-randomized trials, interrupted time series or controlled before-after studies to fill the matrix.

Results: Of 8000 records retrieved only five studies met our inclusion criteria. There is some evidence of consumer involvement in: policy (a single low quality study of community health goals); research (two moderate quality studies); and developing patient information (two moderate quality studies). There is no evidence about the effects of consumer involvement in clinical practice guidelines.

Conclusions: The most striking feature of the matrix is the preponderance of empty cells, where we were unable to identify any studies. The value of the matrix is in identifying several knowledge gaps. Suggestions for further research: a systematic review focusing on any evaluation of consumer involvement in guideline development, to inform the design of trials that rigorously evaluate the effects of consumer involvement in guideline development.

References
1. Nilsen ES, Myrhaug HT, Johansen M, Oliver S, Oxman AD. Interventions for promoting consumer involvement in developing healthcare policy and research, clinical practice guidelines and patient information material (Protocol). In: The Cochrane Database of Systematic Reviews Issue 1, 2004. Chichester, UK: John Wiley & Sons, Ltd.
2. Oliver S, Clarke-Jones L, Rees R, Milne R, Buchanan P, Gabbay J, Gyte G, Oakley A, Stein K. Involving consumers in Research and Development agenda setting for the NHS: developing an evidence-based approach. Health Technology Assessment 2004; 8(15):1-148.