Background: Cochrane Reviews should be, and are being used to inform decisions, both in clinical practice and at policy level. Increasing numbers of reviews are published within certain areas, e.g "Mental health". Users often formulate broad questions involving results from several reviews. Systematic and explicit methods to find, appraise and summarise the evidence from reviews in overviews of overviews (OoO) are needed.

Objective: The aim of this paper is to present a framework for summarising and grading the evidence in overviews of overviews.

Method: When performing OoO the source of information is systematic reviews. Often checklists focus on either the systematic review or the primary studies. Problems arise when the quality of reviews and the quality of studies varies independently. Principles from the GRADE approach were used to developed the suggested framework for grading evidence in OoO. The following factors were taken into account; design of primary studies, quality of reviews and quality of primary studies, consistency of the results in the primary studies and directness.

Result: This framework grades evidence from OoO into four categories, as shown in the table below. The categories arise from combining the quality of the review, the design and quality of primary studies, consistency and directness.

Conclusion: A framework that helps to summarise and grade the evidence in OoO is presented. OoO are limited by the availability of high quality and up to date systematic reviews relating to the questions that need answering.
Reference: Grading quality of evidence and strength of recommendations. The GRADE Working Group. BMJ 2004; 328 (7454): 1490

Grade - Based on:

High quality evidence
One or more updated, high quality systematic review that are based on at least two high quality primary studies with consistent results

Moderate quality evidence
One or more updated systematic reviews of high
or moderate quality
- based on at least one high quality primary study
- based on at least two primary studies of moderate
quality with consistent results

Low quality evidence
One or more systematic review of variable quality
- based on primary studies of moderate quality
- based on inconsistent results in the reviews
- based on inconsistent results in primary studies