Table 22.2.a: Comparison of methods between Cochrane Intervention reviews and Cochrane Overviews of reviews

 

Cochrane Intervention reviews

Cochrane Overviews of reviews

Comments regarding Cochrane Overviews of reviews

Objectives.

To summarize evidence from studies of the effects of interventions.

To summarize evidence from systematic reviews of the effects of interventions.

Appropriate when there are two or more interventions for the same condition or problem presented in separate Cochrane Intervention reviews.

Selection criteria.

Describe inclusion and exclusion criteria for studies.

Describe inclusion and exclusion criteria for reviews.

Primarily only Cochrane Intervention reviews are included. Sometimes Cochrane Intervention reviews and other reviews found in The Cochrane Library (Database of Abstracts of Reviews of Effects or Health Technology Assessment Database) may be included. Occasionally other systematic reviews may be included.

Search.

Comprehensive search for relevant studies.

Typically search for only relevant Cochrane Intervention reviews.

May occasionally search for non-Cochrane systematic reviews.

Data collection.

From included studies.

From included systematic reviews.

If necessary, authors of Overviews may seek additional information from the authors of included systematic reviews or occasionally from the primary studies included in systematic reviews.

Assessment of limitations.

For included studies; i.e. risk of bias.

For included systematic reviews.

Authors of Cochrane Overviews should critically appraise included reviews using explicit criteria. Both general limitations (e.g. whether the review is up to date) and specific limitations should be considered (i.e. if a systematic review has limitations relative to the specific objectives of the Overview).

Quality of evidence.

Across studies for each important outcome.

So far as possible should be based on assessments reported in the included systematic reviews.

It is recommended that each Overview should include an assessment of the quality of evidence for each important outcome. If such an assessment was not done in included systematic reviews, authors of Overviews should try to do it. If it was done in included systematic reviews, authors of Overviews should critically appraise the judgements that were made and try to ensure that these judgements were made consistently across included reviews.

Analysis.

Syntheses of results across included studies for each important outcome.

Summary of review results; additional analyses may be undertaken for comparisons across reviews, typically indirect comparisons of multiple interventions.

So far as possible authors of Cochrane Overviews should rely on analyses reported in the included reviews. Occasionally data may need to be reanalysed, for example if different populations or subgroups are analysed in different reviews and it is possible to undertake comparable analyses across reviews.