South African Cochrane Centre

Why is a systematic review different to a traditional literature review?
Traditional literature reviews are prone to bias in a number of ways. The author of such a review may choose to only include studies which they are familiar with or which support their particular point of view - this is known as selection bias (also called "file-drawer bias"). Authors may choose to include only studies that have been published (publication bias) or only studies written in English (language bias). Limiting searches for studies to certain databases and indexing terms may also introduce a special bias into the review called indexing bias.

A systematic review is more rigorous than a traditional review and attempts to reduce the influence of bias in a number of ways:

• It addresses a clearly formulated question
• It uses systematic and explicit methods to identify, select and critically appraise relevant research
• It uses systematic and explicit methods to collect and analyze data from the studies that are included in the review
• Statistical methods (meta-analysis) may or may not be used to analyze and summarize the results of included studies which are considered similar enough to combine.

How to conduct a systematic review
When one decides to do a review, the first step is to contact the relevant Review Group Co-ordinator (http://www.cochrane.org/contact/entities.htm#CRGLIST) who will register your topic for you. The next stage involves developing a protocol which will be peer-reviewed before you can begin the review itself.

Please see the attached diagram for an outline of the review process.

We at the South African Cochrane Centre can assist you with negotiating the initial stages of this process and will put you in touch with the right people.

How long does it take?
On average a review will take 18 months, but it can be shorter or much longer than this. Once you have published a review, you will be responsible for updating it every two years - your Review Group will assist you in this process.

What's in it for me?
A full review is indexed on MEDLINE and you will be encouraged to submit it for paper publication. High impact factor journals such as The Lancet, the British Medical Journal and our local journal, the South African Medical Journal, have publicly stated that they will endevour to publish relevant Cochrane reviews.