Government Social Research
Last Updated: 16/9/2008
Systematic. A broad review of existing research on a topic and synthesis of the evidence provided by these studies to answer the review question.
Time taken: 8 to 12 months minimum
A full systematic review is the combination of a full evidence map and synthesis. Systematic reviews of evidence have explicit objectives and studies are chosen on explicit criteria. A thorough search for studies is conducted using electronic and print sources and the grey literature (unpublished/work in progress) as well as hand searching journals and textbooks, searching of specialist websites, and use of personal contacts. Each study found is screened according to uniform criteria and the reasons for excluding studies clearly documented (Cochrane Collaboration 2007).
If you have already undertaken a systematic listing of existing research (full analytic map) a post map synthesis can be undertaken in about 4 months.
Systematic reviews are the most robust method for reviewing evidence because they reduce the bias in the way studies are found, included and synthesised. Transparency allows future studies to be added to the review which enables a cumulative body of sound evidence to be developed on a subject area over time. Furthermore, it should be possible for anyone else to conduct the same review and come to the same conclusions.
There is a myth that systematic reviews are only suitable for experimental studies. While it is true that many of the existing systematic reviews have concentrated on large scale quantitative studies, systematic review methods can be applied to any type of question. Where quantitative studies are included it may be possible to undertake a meta-analysis – a method of analysis which combines statistically the results of a number of studies. If more qualitative data are used then a qualitative synthesis can summarise these results. Some reviews do both, and integrate a meta-analysis of data from controlled trials with a synthesis of findings from qualitative studies (Gough & Elbourne, 2002). This is also true for Rapid Evidence Assessments.
The strength of systematic reviews is that they aim to be as comprehensive as possible in the studies they find, include and synthesise. However, this leads to their principle disadvantage, which is that they are time consuming. They also require a team of researchers (either ‘in-house’ or contracted to carry out the work) and are therefore resource intensive (although likely to be less so than undertaking a piece of primary research).
Methods for reviewing evidence index