PubMed: Keyword search

To find articles/document on a topic, enter keywords (search terms) into PubMed's search box. PubMed then searches for documents that include your keywords in their titles, abstracts (summaries) and other key fields. The following steps will help you carefully identify and organise your keywords so that you're more likely to find the best results:

• Identify the words in your assignment/research question that are most relevant to the topic (and distinguish it from any other topic). For an example, let's consider this question: "Investigate the impact of carbohydrate drinks on endurance".
  
  The most important words/phrases are carbohydrate drink, endurance. Generally, it's best to ignore generic words such as 'impact
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• Treat each word/phrase as if it's a "separate" concept within the overall topic. Then, for each concept, identify any alternative words that have the same or similar meaning. Different authors can use different words to describe the same concept so your keywords need to reflect this. Here's a list of keywords, organised by concept, based on our search example: 

Also consider alternative keywords that have the opposite meanings. Above, fatigue is included in relation to endurance.

With some searches, you can increase the number of your results by truncating a word and entering an asterisk at the end of its stem (which should contain a minimum of 4 letters):

e.g. if you enter fractur*, PubMed will search for fracture, fractures, fractured, fracturing.  

However, with other searches, using an asterisk can reduce the number of results! This is because PubMed not only searches across titles and abstracts, but also 'subject headings' which are taken from the MeSH thesaurus and added to individual records. However, if you include an asterisk in your keyword, PubMed won't search for any words/phrases that are recognised by the thesaurus as alternatives for that keyword.

The solution? You could enter your search terms twice, once with an asterisk and once without (in singular form) e.g. fractur* or fracture. If you want to know whether your search term exists as a MeSH term, refer to MeSH tab of this guide and in particular, point 4 in the section, 'How to do a MeSH-only search'.

However, if you're doing a systematic review and you want to apply the most through way of searching PubMed, run your keyword search separately from a MeSH-based search and then combine the two sets of results.

To ensure that PubMed searches for a precise phrase in titles and abstracts (rather than also searching for each word in the phrase separately), you can enter the phrase within "speech marks". However, the use of speech marks prevents PubMed from also searching for your phrase as a potential MeSH Subject Heading so you may want to enter the phrase twice, once with and once without speech marks. PubMed does recognise some phrases without the need for speech marks, but not all: further explanation.

Click the Advanced link just below the search box on PubMed's 'homepage' to take you to the advanced search page.

• Entering alternative keywords: If you've identified alternative search terms for a specific concept within the overall theme of your assignment/research, enter the word OR in between each search term e.g. endur* or fatigue*. Potentially, this will increase the number of your search results.
  
  

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• Using the AND function: if your assignment title/research question has multiple sub-themes, you should enter each corresponding set of search terms separately into the search box (i.e. one set at a time). After entering each set, click the 'Add with AND' button. Your accumulating search terms appear in a 'query' box'. Using the AND option ensures that each of your search results will include at least one search term from each set of terms that you entered.
  
  
  
  

• ​Once you have entered all of your search terms, click Search to get your results.
   

• Too many irrelevant results? Take another look at your keywords and consider whether these should be more precise. Furthermore, if an additional concept needs to appear in each result, add the associated search term(s) as a separate set (again adding it to other sets using AND). 
  
  You could also consider changing the search box's setting from 'all fields' to 'Text word'. This instructs PubMed to only search titles, abstracts, subject headings, substance names and a few other fields in PubMed records.
   

• Too few relevant results? Consider whether any further keywords exist on your topic and if so, add these to the relevant sets of search terms. If the problem remains, and you have entered multiple sets of keyword, try excluding the least essential set.  
   

• Field tags: if you need to see which field tags have been applied to your search by PubMed, scroll down the Advanced Search screen to the 'query' section which lists all the searches you've undertaken in the current search session.

With some searches, it helps to specify that you want two or more keywords to appear in close proximity within the titles or abstracts. This is useful where multiple variations of the same phrase exist e.g. ACL fracture, fractures of the ACL. PubMed offers a limited 'proximity search' option: overview and more details.