The number of published systematic reviews of randomised drug trials has risen rapidly in recent years. This has led to the development of ‘overviews’ of systematic reviews, known as ‘umbrella reviews’. These umbrella reviews are similar to systematic reviews of randomised drug trials, but in this case the basic unit is not the randomised trial but the systematic review. The scope of an umbrella review is usually larger than that of a systematic review, and this can facilitate the formation of judgements about drugs in health care. Guidelines for composing umbrella reviews have been established, which enable readers to assess their quality. Pitfalls include contradictory systematic reviews and overlaps between the studies included in the various systematic reviews.
- Umbrella reviews can save time and can have a larger scope that systematic reviews.
- An inevitable risk and potential disadvantage of umbrella reviews is that they put readers at an even greater distance from the primary studies.
- It is important to always critically assess the quality of umbrella reviews.
- Pitfalls of umbrella reviews include overlaps of included studies and contradictions between the constituent systematic reviews.
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