Umbrella review-a useful tool when it's raining systematic reviews.

Systematic reviews and accompanying meta-analyses of high-quality studies are at the top of the evidence pyramid. By synthesising the totality of evidence they can address a variety of clinical and research questions. Although they were initially effectiveness and safety of health interventions, systematic reviews (with or without meta-analysis) are now also common in the evaluation of diagnostic test accuracy, prognostic factors, prediction models, prevalence of disease, cost-effectiveness and other areas. With increasing numbers of systematic reviews, clinicians, consumers, and policy makers usually need to refer to a large number of systematic reviews to inform clinical decision-making.