The sheer volume of material published in medical journals each week is well beyond any of us to keep up with, and in order to save us from drowning in information the writers of systematic reviews aim to collect together and appraise all the evidence from appropriate studies addressing a focussed clinical question. The Cochrane Collaboration has been working at this task for the past twenty years and, in September 2016, there were 7038 completed reviews on the Cochrane Database of Systematic reviews and a further 2520 protocols that will become reviews in the future.
The File-Drawer Problem
So what was wrong with the traditional narrative review from an expert in the field? The main problem with this approach is that we all have our preferred way of doing things, and there is a natural tendency to take note of articles that fit in with our view. This means that when asked to review a topic it is natural for an expert may quote all the data that supports their favoured approach.
What is a Systematic Review?
So how is a systematic review different? Let’s start with a definition:
Systematic review (synonym: systematic overview): A review of a clearly formulated question that uses systematic and explicit methods to identify, select and critically appraise relevant research, and to collect and analyse data from the studies that are included in the review. Statistical methods (meta-analysis) may or may not be used to analyse and summarise the results of the included studies.
The difference here is that the way the papers were found and analysed is clearly stated.