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Systematic Reviews: Searching

Databases to Search

No one index includes all journal articles so you'll need to search multiple databases. There are three main databases to search:

Depending on your topic you may also want to search:

Grey Literature

Studies reporting negative results are less likely to be published in journals than those reporting positive results.  Including unpublished studies and other grey literature in your review reduces publication bias and may affect your statistical results. 

search.bioPreprint
Searches multiple preprint resources at once including: medRxiv, bioRxiv, ChemRxiv, AAS Open Res, F1000Res, Gates Open Res, HRB Open Res, MNI Open Res, PeerJ Preprints, Preprints.org, Research Square, Wellcome Open Res. 

medRxiv
A preprint server for medical, clinical, and related health sciences. 

bioRxiv
A preprint server for the Life Sciences, including Cancer Biology, Immunology, Pharmacology and Toxicology.

Conference abstracts: should you search them or not? 

Reporting your Search

PRISMA-S Checklist: a guide on how to describe your search strategies in your manuscript

Searching Guidelines

PRISMA-S Checklist a PRISMA checklist of items to include when reporting literature searches in systematic reviews

Standards for Finding and Assessing Individual Studies (Ch. 3 in Finding What Works in Health Care: Standards for Systematic Reviews): instructions for identification, screening, data collection, and appraisal of individual studies

"Searching for and Selecting Studies" (Cochrane Handbook Technical Supplement to Ch 4)  Gives detailed information on which databases to search, how to create search strings, and how to use search hedges and text mining software. Gives examples of search strings and explains truncation, wildcards, boolean search operators, and proximity searching. Provides lists of databases, software recommendations, search examples, and other detailed information.

Search Hedges

Hedges are search strings created by expert searchers to help you retrieve specific types of studies or topics. 

Useful Tools

Yale MeSH Analyzer: Enter up to 20 PMIDS to see a list of MeSH subject headings.

PubMed PubMedReminer:  Enter multiple PMIDs to see a list of MeSH subject headings. Also lists authors, journals, and countries. 

NLM MeSH on Demand:   Enter a paragraph and find the most likely MeSH subject headings to search for additional articles. 

Polyglot Search Translator: Translates a PubMed or Ovid Medline search string to multiple other databases. (Note: translates the format but not the subject headings)

CitationChaser:  enter in an article and get a list of all of the references in it and all of the later articles that cited it.  

Find Existing Systematic Reviews

Before you start a systematic review, it's a good idea to see if one has already been published on your topic.  There are several places to find them: 

Epistomonikas

Searches ten different databases for systematic reviews. 

PubMed

Search for your topic and select "Systematic Review" in Article Types on the left.

PROSPERO

An online registry of systematic reviews currently in progress.

COCHRANE PROTOCOLS

Detailed descriptions of Cochrane systematic review protocols.

Are there enough studies for your topic?

Before you start a systematic review, it's a good idea to do a quick search to get an idea of what kinds of studies and how many studies have been written on your topic. 

Evaluating Search Strings