Aim of the search
The overarching objective of a systematic review search for evidence is to identify all the studies (and all the relevant data from the studies) that pertain to the research question.
Your search plan will be a brief summary of the topic of the study, a summary of inclusion and exclusion criteria, a list of the appropriate publications, sources and methods that you will use for identifying materials and a list of concepts related to your topic. Your search strategy will put into operation the decisions you have made in your search plan.
Begin devising your search strategy by using the PICO for quantitative research and PICo for qualitative research and ensure that the research question has been translated into search concepts.
NOTE: It may be useful to work with a librarian who has experience in a wide range of bibliographic databases and electronic information sources to plan your search strategy.
Step One - Documenting searches
When you are conducting your searches, keep track of what you are doing by documenting your search process in enough detail to ensure that it can be reported correctly in the review.
Documentation of your search strategy should include:
Step Two - Reporting searches
There are a number of places where searches can be reported. These include the appendix, the review abstract, the methods section or the results section. Below are some examples that show these different models:
It is advisable to use the PRISMA 2009 flow diagram for further documentation of the number of records identified by database searching and through other sources. The flow diagram depicts the flow of information through the different phases of a systematic review. It maps out the number of records identified, included and excluded, and the reasons for exclusions.
The aim of the search strategy is to maximise the retrieval of relevant documents and minimise the retrieval of non-relevant material. It is necessary to strike a balance between achieving comprehensiveness and maintaining relevance when developing a search strategy. Increasing the comprehensiveness (or sensitivity) of a search will reduce its precision and will retrieve more non-relevant articles.
Sensitivity is the ability to identify all the relevant studies. Specificity is the ability to exclude irrelevant studies. There is an inverse relationship between sensitivity and specificity i.e. high sensitivity will tend to have low specificity, and this means that a large number of articles retrieved are not relevant to the review question.
Inappropriate or indadequate search strategies may fail to identify records that are included in bibliographic databases.
Revising your search strategy
Your search strategy will have to be revised if:
When to stop searching
There comes a point where the rewards of further searching may not be worth the the effort needed to capture additional references. The call to abort further searching depends on the question a review addresses and the resources that are available. A thorough review of some high quality studies is generally preferable to a less discriminate probe for dubious items.
The PRESS Guideline provides a set of recommendations and a checklist which can be used to evaluate electronic search strategies.
The full guideline statement and checklist document may be accessed via the following open access article from the Journal of Clinical Epidemiology:
McGowan J, Sampson M, Salzwedel DM, Cogo E, Foerster V, Lefebvre C. PRESS Peer Review of Electronic Search Strategies: 2015 guideline statement. J Clin Epidemiol. 2016 Jul;75:40-6. http://www.sciencedirect.com/science/article/pii/S0895435616000585
Search each concept in the research question separately
Use OR between synonyms to broaden the search for each concept
Combine each concept with AND
The key fields to search are the
Subject Heading - use the database headings (eg MeSH or CINAHL headings) to find the subject term
Title OR abstract - use advanced search page to build a search with synonyms for an idea combined with OR
MeSH heading - "Stroke"
TI (stroke OR "cerebrovascular accident" OR "CVA") OR AB (stroke OR "cerebro-vascular accident" OR "CVA")
More detailed searching help can be found on the Advanced Database Searching guide.