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
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
- It uses systematic
and explicit methods to identify, select and critically appraise relevant
- 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
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
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.
long does it take?
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.
in it for me?
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.
once you have published a review you will automatically receive your
own free copy of The Cochrane Library as long as it is updated regularly.