Table 22.1.a: Reasons for overviewing reviews and their suitability for publication as a Cochrane Overview

Objective

Selection criteria

Examples of overviews

Suitable for inclusion as a Cochrane Overview of reviews

Comments

To summarize evidence from more than one systematic review of different interventions for the same condition or problem.

Cochrane Intervention reviews.

A Cochrane Overview of interventions for nocturnal enuresis (Russell 2006) 

Yes.

This is the primary purpose of Cochrane Overviews (and should be referred to as an Overview of Cochrane reviews in the objectives section of the abstract and the text).

Cochrane Intervention reviews and non-Cochrane systematic reviews.

Some BMJ Clinical Evidence chapters and an increasing number of health technology assessment (HTA) reports.

Possibly.

It may sometimes be appropriate to include non-Cochrane systematic reviews as well as Cochrane reviews, for example, if there are important interventions for which good quality systematic reviews have been published and a Cochrane review is not available. However, CRGs are encouraged to focus primarily on Overviews of Cochrane reviews as:

  •  searching for and including non-Cochrane reviews in Overviews entails additional work and challenges

  •  non-Cochrane reviews may not be accessible to users of The Cochrane Library

  • the primary aim of Cochrane Overviews is to summarize Cochrane reviews and to provide a user-friendly front end.

To summarize evidence from more than one systematic review of the same intervention for the same condition or problem where different outcomes are addressed in different systematic reviews.

Cochrane Intervention reviews.

An overview of Cochrane reviews of hormone replacement therapy (HRT) for menopause where outcomes may include bone density, menopausal symptoms, cardiovascular risk/ events, cognitive function etc.

Occasionally.

As a rule, individual Cochrane reviews should include all outcomes that are important to people making decisions about an intervention. However, occasionally, as with HRT, different outcomes have to a large extent been considered in different systematic reviews.

Cochrane Intervention reviews and non-Cochrane reviews.

Some BMJ Clinical Evidence chapters and some HTA reports.

Rarely.

The considerations for including non-Cochrane systematic reviews are the same as those noted above.

To summarize evidence from more than one systematic review of the same intervention for different conditions, problems or populations.

Cochrane Intervention reviews.

An overview of Cochrane reviews of vitamin A for different populations and conditions.

Occasionally.

The same or similar interventions may sometimes be used for different conditions or different studies and reviews may focus on different populations. While an overview of these reviews is unlikely to be of interest to clinicians and patients deciding how best to address a specific problem, an overview may be relevant to policy makers or to addressing questions that cut across the different reviews.

Cochrane Intervention reviews and non-Cochrane reviews.

Rarely.

The considerations for including non-Cochrane systematic reviews are the same as those noted above.

To summarize evidence about adverse effects of an intervention from more than one systematic review of use of the intervention for one or more conditions.

Cochrane Intervention reviews only or Cochrane Intervention reviews and non-Cochrane systematic reviews.

An overview of adverse effects of NSAIDs when used for osteoarthritis or rheumatoid arthritis or menorraghia.

Rarely.

While many Cochrane reviews report on adverse effects, few if any are designed primarily to assess rates of adverse effects. Many important adverse effects occur so rarely that their true prevalence cannot be accurately assessed from results of controlled trials. For these reasons, an overview based solely on Cochrane or other systematic reviews of controlled trials may not give an accurate picture of the adverse effect profile of a specific intervention – unless the systematic reviews it summarizes have been specifically designed to address the rates of adverse effects (see Chapter 14 for further information on the reporting of adverse effects in Cochrane reviews.

To provide a comprehensive overview of an area, including studies not included in systematic reviews.

Systematic reviews and studies not included in systematic reviews.

Some BMJ Clinical Evidence chapters, an increasing number of HTA reports or a synoptic review article for a journal.

No.

Including studies that have not previously been included in a systematic review may be appropriate in a number of circumstances, for example when undertaking a HTA report, developing a clinical practice guideline, or for resources such as BMJ Clinical Evidence. However, this is beyond the scope of what should be done in a Cochrane Overview. Authors of Cochrane Overviews should note when included reviews are out of date, particularly if new relevant studies have been published, and if there are relevant interventions for which a systematic review has not yet been published. However, they should not undertake an update of a systematic review or a new systematic review within the Overview.