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Physician Associates research project guidance: Doing a structured literature search

Resources and links to guide you through your research project.

Doing a structured literature search

Although all projects require a search of the literature, with this type of project it is beneficial to be much more thorough and structured in the way you approach your search and manage the results. This could include the following:

  1. Identifying all relevant keywords used to describe the topic and limits to apply.
  2. Deciding where to search.
  3. Building a search strategy to include all the alternative keywords and adapting it for for different databases.
  4. Running the search on each databases, downloading the results to a reference manager and deduplicating (you may find the same article appears on multiple databases). Filtering the results by evaluating each study for relevance - title/abstract filtering initially, followed by full-text.
To review your topic you will need to have identified the key publications in the field and therefore a structured approach to searching the literature is beneficial. The papers you use to help answer your questions may require you to compare results from core papers in depth and therefore you should make sure you are working with only 5-15 papers. However, you may be using multiple sources to demonstrate breadth of our understanding of a topic to answer your question and therefore your results will touch on a wider breadth of papers. Your search method will need to align to the needs of your review.  

1. Decide where to search - use the key database plus at least one other from this list

Key database
Additional relevant databases

If you wish to extend your search further you might want to explore these databases.

2. Identify relevant keywords and inclusion/exclusion criteria

Before you start you MUST carefully consider what words you need to include in your search. Think about...

  • synonyms
  • abbreviations
  • related terms
  • UK/US spellings
  • singular/plural forms of words

To get started try a search for your basic keywords on Summon, the Library's discovery service. Look at the title, abstract and keywords in any relevant articles - what other terms are used to describe your concepts? Add them into your list of alternatives.

Use the template below to analyse your topic - breaking it down into separate concepts, working out alternatives for each concept, and deciding on any limits. Discuss this with your supervisor.

Inclusion / Exclusion criteria

How are you going to decide which papers should be included in your study? Create a list of inclusion and exclusion criteria. This could include the following:

  • dates - are you only looking for recent papers?
  • study type - are you only looking at papers describing randomised controlled trials for example?
  • population - does the article discuss the right section of the population e.g. elderly, children, infants
  • intervention - if you are looking at a specific treatment are the studies discussing the right form of treatment 

It might be possible to include some of these limits in your search e.g. applying date limits, or article type limit on PubMed. Or you might be able to build it into your search e.g. RCT* OR "randomi?ed control* trial*".

But mostly you will use your inclusion and exclusion criteria to judge each article, firstly by reading the title and abstract, and then by reading the full articles of those which appear to be relevant. This will enable you to filter your results down to the most relevant studies.

Discuss your inclusion and exclusion criteria with your supervisor.

3. Build a search strategy

The following techniques work on most databases to build a comprehensive search.

Truncation and wildcards

Although databases have developed, and some will automatically search for variant spellings and plurals, mostly they will just search for the exact letters you type in. Use wildcard and truncation symbols to take control of your search and include variations to widen your search and ensure you don't miss something relevant.

  • A truncation symbol (*) retrieves any number of letters - useful to find different word endings based on the root of a word
    medic* will find medic, medics, medicine, medicinal... and any other words beginning with medic

  • Wildcards can be used to stand for one or no letters within a word. They can be useful for retrieving alternate spelling spellings (i.e. British vs. American English) and simple plurals Wildcard symbols vary between databases - check the help. PubMed does not support wildcards. The following work on Web of Science:
    - the wildcard symbol (?) replaces a single letter e.g. wom?n will find woman or women
    - the wildcard symbol ($) stands for one or no letters e.g. behavio$r will find behaviour or behavior

Search operators

Search operators control how your words are combined. Using operators means you can search for all of your terms at once rather than carrying out multiple searches for each alternative.

There are three main operators:

  • OR - for combining alternative words for your concepts and widening your results e.g. children OR infants OR babies
  • AND - for combining your concepts giving more specific results e.g. children AND autism AND diet
  • NOT  - to exclude specific terms from your search - use this with caution as you might exclude relevant results accidentally! e.g. children NOT babies
Phrase searching

If you have words you want to search for together, as a phrase, you can specify this by enclosing them in double quotation marks e.g. "crohn's disease". This makes your search more specific, will reduce the number of results you find and increase the relevance. Note that on Scopus instead of using quotation marks you use these brackets {   } e.g. {crohn's disease}.

Creating a search statement

Once you have all your keywords and their alternatives you can build a search statement like this:

("mental health" OR depress* OR "mental disorder*" OR stress) AND ("inflammatory bowel disease" OR "ulcerative colitis" OR "crohn's disease")

Note the way the sets of alternative words combined with OR are enclosed in brackets. This ensures correct processing of the search.

On PubMed you can use the Advanced search to build the statement for you. On Web of Science and Scopus you could use the Add row/Add Search Field option to enter each set of keywords in separate boxes and it will insert the AND operator and brackets for you.

Watch this video for a demo of using these techniques (skip to 3 min 43 sec)
Tips on searching PubMed

PubMed will do a lot of clever processing of your search. Each article on PubMed is assigned Medical Subject Headings (MeSH) to describe what it is about. If one of your words or phrases matches on a MeSH heading it will automatically include all articles using that term and may also include more specific terms which come under that heading. Using quotes for phrase searching and truncation will stop this automatic mapping onto MeSH terms, so on PubMed you may find you get more results by not using these techniques.

Watch these videos for an introduction to searching PubMed.

Taking control of your PubMed search

There are specific ways to enter a search on PubMed to ensure you take advantage of the Medical Subject Headings as well as including all the alternatives you need. Watch this video by by John Hopkins University which explains how to use specific fields when building your search.

See the PubMed user guide for more information on searching:

Applying limits

It might be possible to use the limit options on databases to apply some of your inclusion/exclusion criteria to your search results. Standard ones available on all databases include:

  • Date limits - use to omit older articles
  • Document type - just articles?
  • Language - just English?

On PubMed it is also possible to limit in additional ways:

  • Article type - RCTs, meta-analysis, systematic review
  • Age group - children, adults, elderly (and more specific ones)
  • Species - humans vs animals

If it is not possible to apply a limit on the database you are using you might need to add an extra concept to your search statement. For example, when searching Scopus if you are only interested in RCTs you will need to add an extra element to your search to cover this (RCT* OR "randomised control* trial*" OR "randomized control* trial*")

4. Run the search on each database, download the results to EndNote and deduplicate

It is important to keep an accurate record of your searches as this will help you plan and revise your search. 

  • Keep a record of the date you searched, the name of the database, and the platform.
  • Record the exact search you ran and any limits you applied. You might be able to download your search history from the database. 
EndNote logoManaging your search results

Once you have finalised your search statement you should aim to run the search on your chosen databases on one day and download the results to a reference management tool. EndNote is recommended because...

  • When searching you can export your search results directly into EndNote.
  • Once you have collected all the references from the relevant databases you can automatically de-duplicate them.
  • In Desktop EndNote the Find Full text feature can be used to automatically source many of the full-text articles.
  • Use the Groups feature to create sub-sets of references.
  • Use EndNote's custom fields to record your decisions about each paper.
  • Numbers derived from EndNote can populate the PRISMA flowchart (see below) when reporting your results.
Not used EndNote before?

Download it and use the guidance via the link below to learn how to use it.

Using EndNote to manage the results of your searches

See the video and guide below for step-by-step instructions on using EndNote to manage the results of your literature searches for your critical review. Although they refer to doing a systematic review, following the same process for managing and analysing the literature for your critical review will ensure you use a structured approach.

Support from your librarian

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Jackie Skinner
Book an appointment
Please contact me if you have a query about literature searching, accessing resources, referencing or using EndNote/Mendeley.

Use the buttons above to email me or make an appointment (in person or online).
Quick query in term-time? Come along to my weekly drop-in on Tuesdays 13:00-14:00 in Harry Nursten Room 2-64. I am also usually on the Study Advice and Academic Liaison Desk on the Ground Floor of the Library on Tuesdays 11:00-12:00.

Using the PRISMA flow diagram to record the search and filtering process

PRISMA flow diagram example

A PRISMA diagram, such as the one shown above, is a standard way to record the number of records retained at each step in the literature search and review process. Download a template using the link below. Use the first template on the page if you are only searching databases. If you are finding references by searching Google, Google Scholar or via citations in key papers you will need to use the second template on the page.

Jump to around 1 minute 18 seconds in to this video for an explanation of filling in the PRISMA flow diagram:

Getting hold of articles

Map of the south of the UK

If you are unable to access the full-text of articles you need for your project we can usually get them from another library via our inter-library loans service. You can request up to 10 articles from this service. On filling in the request form you will usually receive the article by email within a couple of days.