It is important to conduct a thorough search to minimise the risk of missing studies that meet the inclusion criteria. A number of techniques can be used to identify studies: searching bibliographic databases, scanning references lists of included studies, citation searching, searching the internet, & contacting authors of key papers. As you search, keep a record of the databases and other resources you've searched, the search strategy for each resource, the number of results found and the date the search was conducted.
Cochrane Handbook see chpt 4, “Searching for and Selecting Studies” (pp. 67–107). The Technical Supplement which goes into greater detail about searching for and selecting studies. The Appendix of Resources lists databases and other tools used to complete SRs
Bramer, W., de Jonge, G., Rethlefsen, M., Mast, F., & Kleijnen, J. (2018). A systematic approach to searching: An efficient and complete method to develop literature searches. Journal of the Medical Library Association, 106(4), 531-541. https://doi.org/10.5195/jmla.2018.283
Cooper, C., Booth, A., Husk, K., Lovell, R., Frost, J., Schauberger, U., Britten, N., & Garside, R. (2022). A tailored approach: A model for literature searching in complex systematic reviews. Journal of Information Science, , 16555152211144. https://doi.org/10.1177/01655515221114452
European Network for Health Technology Assessment. (2020. Process of information retrieval for systematic reviews and health technology assessments on clinical effectiveness. Version 2.0. https://www.eunethta.eu/wp-content/uploads/2020/01/EUnetHTA_Guideline_Information_Retrieval_v2-0.pdf
Finding What Works in Health Care: Standards for Systematic Reviews see chpt 3, “Standards for Finding and Assessing Individual Studies” (pp. 81–153)
Klerings, I. et. al. (2023). Rapid reviews methods series: Guidance on literature search. BMJ Evidence-Based Medicine. https://doi.org/10.1136/bmjebm-2022-112070 (see Appendix C which contains a worked example and lots of practical advice)
PRISMA-S checklist a checklist for reporting literature searches in systematic reviews
Rapid Reviews see: Klerings, I., Robalino, S., Booth, A., Escobar-Liquitay, C. M., Sommer, I., Gartlehner, G., ... & Waffenschmidt, S. (2023). Rapid reviews methods series: Guidance on literature search. BMJ Evidence-Based Medicine. https://doi.org/10.1136/bmjebm-2022-112079
Health
Cochrane Handbook See Chapter 4: “Searching for and Selecting Studies”
CRD’s guidance for undertaking reviews in health care
JBI Manual for Evidence Synthesis
Not all parts of the PICO question are equally useful and the Outcomes can often be left out of a search:
Frandsen, T. F., Nielsen, M. F. B., Lindhardt, C. L., & Eriksen, M. B. (2020). Using the full PICO model as a search tool for systematic reviews resulted in lower recall for some PICO elements. Journal of Clinical Epidemiology, 127, 69–75. https://doi.org/10.1016/j.jclinepi.2020.07.005
Economics and Business
Geyer-Klingeberg, J., Hang, M., & Rathgeber, A. (2020). Meta-analysis in finance research: Opportunities, challenges, and contemporary applications. International Review of Financial Analysis, 71, Article 101524. https://doi.org/10.1016/j.irfa.2020.101524
Havránek, T., Stanley, T. D., Doucouliagos, H., Bom, P., Geyer‐klingeberg, J., Iwasaki, I.,Reed, W. R., Rost, K. & van Aert, R. (2020). Reporting guidelines for meta-analysis in economics. &Journal of Economic Surveys, 34(3), 469–475. https://doi.org/10.1111/joes.12363
Kraus, S., Breier, M., & Dasí-Rodríguez, S. (2020). The art of crafting a systematic literature review in entrepreneurship research. International Entrepreneurship and Management Journal, 16(3), 1023–1042. https://doi.org/10.1007/s11365-020-00635-4
Education
Alexander, P. A. (2020). Methodological guidance paper: The art and science of quality systematic reviews. Review of Educational Research, 90(1), 6-23. https://doi.org/10.3102/0034654319854352
Engineering
Kitchenham, B., Pearl Brereton, O., Budgen, D., Turner, M., Bailey, J., & Linkman, S. (2009). Systematic literature reviews in software engineering: A systematic literature review. Information and Software Technology, 51(1), 7–15. https://doi.org/10.1016/j.infsof.2008.09.009
Social Sciences
Dacombe, R. (2018). Systematic reviews in political science: What can the approach contribute to political research? Political Studies Review, 16(2), 148–157. https://doi.org/10.1177/1478929916680641
Zawacki-Richter, O., Kerres, M., Bedenlier, S., Bond, M., & Buntins, K. (2020). Systematic reviews in educational research: Methodology, perspectives and application. Springer.
Petticrew, M., & Roberts, H. (2008). Systematic reviews in the social sciences: A practical guide. John Wiley & Sons.
Papaioannou, D., Sutton, A., Carroll, C., Booth, A., & Wong, R. (2010). Literature searching for social science systematic reviews: consideration of a range of search techniques. Health Information & Libraries Journal, 27(2), 114–122. https://doi.org/10.1111/j.1471-1842.2009.00863.x
1. Planning and preparation: Consider using PRISMA-S checklist and consult the relevant subject librarian for your discipline.
NOTE: if you are doing a SR on a health topic, at a minimum you must search: Medline (or PubMed), Cochrane Database of Systematic Reviews, and Central. Depending on your topic you might search additional databases.
2. Scoping search: Run a quick search to identify potentially relevant literature. This will assist in refining the question, selection of appropriate databases and search terms. If your SR is in the health sciences, check a few of the articles in the YALE MeSH Analyzer, see the box below.
3. Construct a search strategy using the search syntax of each database and include appropriate synonyms. If the database uses subject headings, use a combination of relevant subject headings and keywords.
4. Search filters may be appropriate if you want to limit to specific methodologies or population groups (see ISSG Search filters)
5. Save search strategy (see instructions 'Saving your search strategies' box below)
6. Run search and adapt syntax to features of each individual database
7. Exports results to a reference manager, for example, EndNote or Zotero
8. Remove duplicates - see Bramer et al. (2016) for a deduplication method using EndNote
9. If you are using screening software, export results to your chosen program, for example, Covidence
Many databases use Subject Headings as an aid to searching. Subject headings describe the content of an article, each article might have multiple headings. Subject headings are specific to each database. A comprehensive search will use both subject headings and keywords for each concept.
MeSH (Medical Subject Headings) are used in Medline, PubMed and the Cochrane Library.
Yale MeSH Analyzer a useful tool to identify search terms (keywords and subject headings) from Medline see this introductory video
Document your search strategy and include it in your systematic review so it can be reproduced for verification. For each database, record:
– The database name and platform, for example, Medline (Ovid)
– Date search was run
– Full search strategy, including limits used and date range
– Number of studies found
Save the search strategy in each database with the ‘save search’ feature. You may need to rerun the search strategies if the original search was run more than 12 months before completion of the SR. Consider saving searches as Alerts.
Templates, like the Search Results Summary (from Cochrane’s EPOC resources for Authors) are a useful tool to record search strategies.
| Subject area | Databases |
| Economics/Business |
Scopus Business Source Complete JSTOR Google Scholar |
| Education |
Education Source PsycINFO ERIC |
| Engineering |
Compendex IEEEXplore Scopus ASCE Research Library Google Scholar |
| Health Science |
Key databases: Cochrane Central Register of Controlled Trials (CENTRAL), Medline, EMBASE Clinical trial registers: see Grey Literature for Health Subject specific databases: PsycINFO, CINAHL, SPORTDiscus Citation Indexes: Scopus, Google Scholar |
| Social Sciences |
Scopus JSTOR Political Science Complete SocINDEX |
If you would like to narrow your search to a particular population or by a particular methodology the ISSG (InterTASC Information Specialists' Sub-Group) have a list of appraised search filters ISSG Search Filters Resource NOTE: some of the filters are several years old and might be out of date.
SuRe Info (Summarized Research in Information Retrieval for HTA) contains resources and tips for searching for systematic reviews in health sciences and health technology assessments. Includes: sources to search, designing search strategies, search filters, documenting and reporting the search process and more.
Some filters can be 'launched' in Medline and EMBASE. This means you won't have to type in each line of the search filter into your search.
If you're looking for a Medline RCT search filter, this article reviews a range of filters:
Glanville J, Kotas E, Featherstone R, Dooley G. (2020). Which are the most sensitive search filters to identify randomized controlled trials in MEDLINE? Journal of the Medical Library Association, 108(4), 556-563. https://doi.org/10.5195/jmla.2020.912
LitSense allows you to search for sentences from over 30 million biomedical publications. It can be a useful way to find a few relevant studies which might help with identifying and refining your search terms. It searches not just PubMed, but full text records. When you search, LitSense will find the best-matching sentences.
While it should not be relied on alone for systematic reviews, the Cochrane Handbook states Google Scholar can be used a replacement for the Web of Science or Scopus. There are, however, some limitations with Google Scholar: it retrieves more duplicates than Scopus and frequently the references will need some correcting.
Haddaway, N. R., Collins, A. M., Coughlin, D., & Kirk, S. (2015). The role of Google Scholar in evidence reviews and its applicability to grey literature searching. PloS One, 10(9), e0138237. doi:10.1371/journal.pone.0138237
Gusenbauer, M., & Haddaway, N. R. (2020). Which academic search systems are suitable for systematic reviews or meta-analyses? Evaluating retrieval qualities of Google Scholar, PubMed, and 26 other resources. Research Synthesis Methods, 11(2), 181-217. https://doi.org/10.1002/jrsm.1378