Familiarisation
Do not be afraid to contact the requester with any queries that may arise when you are searching.
Be sure to keep a record of the search strategies you use. Record any assumptions you have made about the search topic also.
Whatever kind of search you are undertaking, broadly follow the steps of this validated guidance, to help ensure you are searching thoroughly:
Even though these examples are intended for full-blown systematic review searches, they can still provide useful guidance for more casual searches.
If you are unfamiliar with the topic, a broad background search using sources such as Google and Wikipedia to familiarise yourself with it.
You will of course need to be mindful of the quality and provenance of the information you see (check references in Wikipedia entries, for instance).
Scoping search
Try a quick scoping search to get a sense of what is out there, to help find keywords and potentially useful evidence.
This could be:
- a quick Google search perhaps entering your requester’s question or topic almost verbatim (copying and pasting it word-for-word)
- entering a few key terms into the Trip Database or Pubmed
- a quick search of the NHS Knowledge and Library Hub
- searching across all databases in one of the provider interfaces simultaneously without specifying any field to search or by title field only
The latter should retrieve only relevant articles that will be indexed with useful terms you can use in your search strategy, as well as variant terms, synonyms etc.
Searching the evidence
Take a top-down approach to searching the evidence, unless advised otherwise within this document, looking for:
- high tier evidence (like reviews in The Cochrane Library)
- entries in clinical decision suport tools: BMJ Best Practice, UpToDate (££), DynaMed (££) or Visual Dx (££)
- primary research (in Medline and other bibliographic databases via the provider interfaces).
If you can find recent high tier evidence this may preclude searching for primary research yourself.
However, in most cases you will need to continue searching to retrieve the most current research.
See high tier evidence sources in the glossary and "High tier evidence sources" in "Quick links" for more information.
Formulate a search strategy, using PICO or another framework if appropriate, to identify the key concepts in the search.
Find natural language terms for each key concept, including rough/exact synonyms. Consider the following:
Variant terms
What we commonly call cancer could also be known as carcinoma, tumour/tumor, neoplasm etc.
Terminology
Differences in US and UK English terminology and spellings, i.e. physiotherapy (UK) vs “physical therapy” (US); or hemorrhage (US) vs haemorrhage (UK).
Wildcards
Using wildcard truncation to retrieve results where different permutations of a word’s root are used, i.e. cancer* retrieves results featuring the terms cancers, cancerous, etc.
Adjacency
Adjacency operators: these vary depending on the interface, but allow you to specify if you want to retrieve results where terms appear NEXT to each other or NEAR to each other.
In the Cochrane Library, for instance, searching for air NEXT pollution retrieves any results where those 2 words appear next to each other, while air NEAR/3 pollution retrieves results where those two words appear within 3 words of each other (in any order).
Phrase searching
Some interfaces perform phrase searching automatically, but most require you enter terms in inverted commas/speech marks to retrieve only the results where your terms appear in the exact order you have specified.
Searching the Cochrane library for “testicular cancer” will only return results where that exact two-word phrase is used, while searching for those terms without the inverted commas retrieves any and all results where those two words appear, but not necessarily together.
Subject headings
For each key concept, find relevant subject headings (including floating subheadings) using your scoping search findings and the “map to thesaurus” function in database interfaces.
How you do this will vary slightly depending on the interface you are using, so check the local help available within the interface.
Check the “scope notes” by subject headings where available, to ensure that the term means what you think it means. These explanations may provide you with more synonyms to introduce to your search strategy too.
Explode subject heading searches wherever possible, to include potentially relevant articles indexed with narrower subject headings.
Include all subheadings within your subject heading searches unless your topic clearly indicates using specific ones.
Boolean operators
Use OR operator to combine synonymous searches to ensure the sensitivity of your search, increase your yield and ensure you are not missing any relevant results.
Use the AND operator to combine the separate concepts in your search, to decrease your yield, increase the specificity of your search and ensure you are returning only results relevant to you.
Search strategy
Adopt a sensitive/broad/inclusive approach to the search, at least initially; you do not want to miss anything important. You can adjust the specificity/sensitivity as you go.
Be wary of using the “major” focus when using subject headings as this may exclude relevant results.
Try and avoid using the NOT operator as this may exclude potentially relevant results from your search's yield.
Screen results for relevance, “sense checking” as you go to see if what you are retrieving is in the right area. Iterate your search strategy if necessary.
Adapt your strategy for other databases and sources. Note that subject headings used in a database will be specific to that database.
Keywords and natural language search elements can be copied and pasted, but subject headings should be searched for afresh.
Add limits to your search as agreed with the requester – but consider if limits by date, language, document type and other parameters etc. are justifiable.
Try a prospective citation search of key articles that you have found or that your requester has provided by searching for them by title in a citation index like Scopus (££), if you have access.
You can do this in PubMed or Google Scholar, checking their “cited by” or “citations” entries, though neither of these is 100% comprehensive.
Citation searching can help you uncover papers that you may otherwise have missed. It is also a test of the rigour of your search: if your search strategy is robust you should retrieve all the papers that the key articles have been cited by. If you have not, consider why not and go back to the drawing board if required.
Most searches will require, or are improved with, an advanced Google search, which can retrieve guidance and policies from NHS Trusts and Integrated Care Boards (ICBs, formerly Clinical Commissioning Groups, CCGs) and other sources, as well as grey literature.
Looking beyond bibliographic databases for grey literature is especially important when searching for evidence around health inequalities, owing to underrepresentation of some groups in the literature.
It can be difficult to judge the quality of Google results, so an advanced Google search using limits will allow you to search within trusted organisations only.
For more help with formulating search strategies and using searching techniques, please see General Help or Troubleshooting.
Thames Valley, Wessex and South West healthcare librarians’ guidance The Literature Search Process: Guidance for NHS Researchers.
E-Learning for Healthcare: How to Search the Literature Effectively.
If you are struggling to create a search strategy or have other searching related queries you can always send an email to one of the mailing lists, where colleagues will be able to help: see mailing list enquiries.