9.1.1 - Why an umbrella review?

Considering the large numbers of systematic reviews and research syntheses available to inform many topics in health care, systematic reviews of existing reviews are now being undertaken to compare and contrast published reviews and to provide an overall examination of a body of information that is available for a given topic (Hartling et al. 2012).  

Conduct of an Umbrella Review offers the possibility of addressing a broad scope of issues related to a topic of interest. The wide picture obtainable from the conduct of an Umbrella Review is also ideal in highlighting if the evidence base around a topic or question is consistent or if contradictory or discrepant findings exist, and in exploring and detailing the reasons why. Investigation of the evidence with an Umbrella Review allows assessment and consideration of whether reviewers addressing similar review questions independently observe similar results and arrive at generally similar conclusions. Reviews of systematic reviews are referred to by several different names in scientific literature as: umbrella reviews, overviews of reviews, reviews of reviews, a summary of systematic reviews and also a synthesis of reviews. In essence however they all have the same defining feature: a systematic review is the main and often sole “study type” that is considered for inclusion (Becker and Oxman 2011; Hartling et al. 2012; Smith et al, 2011).

For JBI syntheses of existing systematic reviews, the term “Umbrella Review” will be used. JBI Umbrella Reviews are designed to incorporate all types of syntheses of research evidence, including systematic reviews in their various forms (effectiveness, meta-aggregative,  integrative, etc.) and meta-analyses.

Beyond the impetus for Umbrella Reviews which is driven by the sheer volume of systematic reviews being published, the need for “fast” evidence in reduced timeframes has also reinforced the attractiveness of undertaking such a review. Decision makers are increasingly required to make evidence informed policy decisions and often require evidence in short timeframes – as a result, “rapid reviews” are also appearing in research literature. Rapid reviews are essentially a streamlined approach to evidence synthesis in health care that attempt to accommodate an evidence informed decision as quickly as possible (Kangura et al, 2012).  While the conduct of a rapid review may impinge on, or result in, undesirable modification of some of the processes required of a well- conducted systematic review, this may be alleviated to some extent by considering if any existing systematic reviews on the topic of interest are already available.

Using existing systematic reviews also reinforces the necessity for some measure of efficiency in scientific undertakings today. In short, if current, multiple, good quality, systematic reviews exist about a given topic or question, any reviewer should reconsider the need to conduct yet another review addressing the same issue. Rather, these may be the basis to conduct an Umbrella Review and summarize or synthesize the findings of systematic reviews already available.