systematic review (of health care) a process of critical appraisal that evaluates the nature of the evidence in support of a treatment against the following test questions. Does it work (its efficacy)? How well does it work (effectiveness)? Is this the best of the available treatments in terms of cost-benefit? And also, can it be made available to those at risk, is it what people want and is it appropriate to their clinically-defined need? The research evidence in support of the treatment is evaluated against the following hierarchical order of strength of evidence: randomized clinical trials, robust experimental studies, robust observational studies, expert opinion and the endorsement of respected authorities. A number of factors underpin systematic review: the need to remove ineffective treatments, the need to establish scientifically agreed criteria for the introduction of new treatments, the need to demonstrate clinical effectiveness through the measurement of outcome and to provide a research-based system for resource allocation in treatment (see I. Crombie (1996) The Pocket Guide to Critical Appraisal, BMJ, London).