Creative Commons Image (CCO)
A systematic review is a very specific approach to searching for literature which seeks to find all studies which have been published and which meet the review's eligibility criteria. A true systematic review should include clear objectives with eligibility criteria for inclusion; a methodology, which it should be possible to replicate; critical appraisal of the findings of included studies; and a systematic presentation and synthesis of the findings of the selected studies (Higgins & Green, 2011). If you are not sure whether you need to do a systematic review or just a literature review, here is a useful guide which will help you decide, produced by Covidence (a company who provide systematic review software).
In the words of the Cochrane Handbook,
"A systematic review attempts to collate all empirical evidence that fits pre-specified eligibility criteria in order to answer a specific research question. It uses explicit, systematic methods that are selected with a view to minimizing bias, thus providing more reliable findings from which conclusions can be drawn and decisions made"
Here is a useful video from Rachael McCool at York Health Economics Consortium outlining the differences between the types of review:
Cochrane have created a free online course available for those who want to learn more about conducting systematic reviews, entitled Conducting an Intervention Review. Developed by world-leading experts, this course provides over 10 hours of self-directed learning on the complete systematic review process for both new and experienced review authors. It is available here.
There are more useful definitions of different types of systematic review linked to on the Glasgow Caledonian University website.
References
Antman, 1992, Oxman, 1993 (cited in Higgins & Green, 2011, section 1.2.2).
Higgins, J.P.T. & Thomas, J. (Eds.). Cochrane Handbook for Systematic Reviews of Interventions Version 6 (updated October 2019). The Cochrane Collaboration, 2019. Retrieved from: https://training.cochrane.org/handbook/current
At this stage in the process, good record keeping is vital. You will need to keep an up to date and accurate list of searches run against keywords and how many results each line of your search strategy produced. Because new articles are always being added to databases, always keep a record of the dates you ran your searches. Because accuracy is so important, it is a good idea to write up your searches as you run them.
Some databases enable you to register your own account so that you can save searches to retrieve them later and also set up alerts to be informed of new articles which are added to the database which match your search criteria.
If the database you're using has a Search History function like CINAHL, this will enable you to easily combine different lines of your search strategy. For more information on this functionality, see the CINAHL help pages.
Once you have decided which studies are to be included in your systematic review report, you will need to critically appraise their quality. There are a number of tools available which will help you to do this, including:
You will also need to pull your findings together, or "synthesise" them. You may choose to do this using narrative synthesis, if you are dealing with qualitative research or statistical synthesis, if you are dealing with quantitative research. There are two chapters in York University's Centre for Reviews and Dissemination guidance for systematic reviews which will be of great help with this process:
Centre for Reviews and Dissemination. (2009). Systematic Reviews: CRD’s guidance for undertaking reviews in health care. York: CRD, University of York.
When writing up your research, there are a number of models you can use to guide your reporting process
Before you start searching you will need to develop a detailed search protocol. Your search will need to aim for high sensitivity, in other words, it needs to be a very broad, comprehensive search which covers all possible terminology. This will mean a corresponding low level of precision, or relevance.
Scoping the review in detail is crucial, for example what population is of interest and within that population what age group? How far back in time do you need to go? You will also need to identify all the databases and other sources of literature which are relevant to search, including grey literature. At the scoping stage it is important to run preliminary searches to identify some key papers which are relevant to the review.
You will need to turn your question into a search strategy which uses both free text and thesaurus terms, having first ensured that you have read and understood any proposals or protocols which have been agreed for the review. You may find it helpful to use a tool to structure your search strategy such as PICO or SPIDER.
It is a good idea for more than one person to be involved with drafting the search strategy and it should always be checked to ensure that it retrieves key papers which have already been identified at the scoping stage. The strategy can then be revised before the full search is run. Once you have identified a strategy which works for one database, you can adapt it for other databases.
For help with search strategies, here are some useful links:
To manage your results effectively, we recommend that you use a reliable reference manager. As well as providing a good place to store your references and organise them thematically, reference management software has a deduplication tool which will be invaluable to you as you will be using multiple databases to run your systematic review, so some duplication of results is inevitable.
More information is available from our reference management guide.
Bryony Ramsden and Kate McGuinn are available to advise on search strategies for systematic reviews but, due to time constraints, are not currently able to take part in the systematic review process. If you need further help, the following links and information may be of assistance.
