Clinical Guides: Literature Searching: Find terms

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Overview

Next, find relevant search terms and synonyms that describe each key concept of your question. An effective literature search combines both keywords and subject headings for each concept.

This is a crucial stage in operationalising your research question, converting it from a mere question into a search. The search terms that you gather at this stage will be used to locate relevant papers from among many millions of published articles.

Key steps at this stage

Find keywords for each key concept
Find subject headings for the database you intend to search
Combine search terms using AND and OR
Consider pre-built searches -- for Intermediate / Advanced searchers, or those conducting a very quick search on a common topic such as a NSQHS Standard. Pre-built searches also exist for specific study designs, such as RCTs and systematic reviews.

Step-by-step worksheet

As you find keywords and subject headings, record them in the Library's worksheet. The appendix includes real-world examples.

Worksheet - Literature Searching: Step by step

The short video below demonstrates how you can use the table on p. 3 of the worksheet to record search terms for each of your concepts.

Using keywords and subject headings [3 mins, 47 secs] by University of Sydney Library

Find keywords

What are keywords?
Keywords are simply words and phrases that describe the key concepts in your research question. For instance, if you are searching for papers on COPD, keywords for this condition would include chronic obstructive pulmonary disease, COPD, and emphysema.

How are keywords used in searching?
When you search a literature database using keywords, the database will look for papers which include your keywords. In scholarly literature, keywords are found in places such as the title of a paper, the abstract, and any keywords provided by the author(s).

Note: Most databases are not able to search for keywords within the body of the article, i.e. they are not searching the full-text but rather the sections listed above.

How to find keywords

Start brainstorming keywords by drawing on your existing subject knowledge and the background research that you completed in Developing your question. Remember to focus on relevant keywords only -- stay within the scope of your research question.

Additionally, you can find keywords by utilising the methods below.

Beginner methods

Check medical dictionaries, thesauri, and encyclopaedias (search the Library catalogue).
Look up your concepts in a general textbook (search the Library catalogue) or clinical decision support tools to see how they are described and referred to.
Review relevant articles on your topic. If you already know of a few relevant papers, check them to see:
- which keywords and phrases the author(s) have used in the title and abstract
- if there are any author-provided keywords listed -- these are often found beneath the abstract
Use text mining tools -- see more information below.

Intermediate / Advanced methods

Look up known relevant articles in a database such as Ovid MEDLINE and view the 'Complete reference' to see its assigned keywords.
Search the MeSH database for your topic and look for additional keywords under 'Entry terms' and 'Scope note' (view COPD example).
Read published systematic reviews on the topic. Many are required to include a copy of their search strategies. At the very least, the methodology will often list keywords used in the search.

Include synonyms & variants

It's important to remember that not all papers use exactly the same terminology (i.e. the same keywords or phrases) to describe the same phenomenon or research area. We need to think of the different words that authors might use for the concepts for which we are searching, and incorporate a variety of relevant keywords into our search.

When gathering keywords, consider the following:

Alternate spelling	pediatric or paediatric
Alternate ending	hospital or hospitalised or hospitalisation (or hospitalization)
Word form	physiotherapy or physio therapy
Plural form	child or children, woman or women
Acronym	Severe Acute Respiratory Syndrome or SARS
Abbreviation	electronic cigarettes or e-cigarettes
Terms that mean the same thing	Cancer or neoplasms or tumour or tumor or carcinoma

Use text mining tools

You can use text mining tools to find frequently occurring keywords and phrases in the literature, including synonyms for keywords that you have already identified. Text mining tools are usually free, quick, and easy to use.

Beginner tools

These tools use keywords to create visualisations such as word clouds:

Carrot2 - search for a keyword to get a quick visual overview of available information, grouped into topics. Limit the search to PubMed (rather than 'Web') to focus on medical literature.
PubVenn - generate Venn diagrams based on keywords. It also links to articles within the PubMed database.

Intermediate / Advanced tools

The following tools require you to input known relevant articles and/or an existing PubMed search:

Yale MeSH Analyzer - upload PMIDs to create a grid of MeSH terms and author keywords from individual papers.
PubMed Reminer - provides analysis in a tabular format showing the frequency of terms and MeSH headings from search results.
Voyant Tools - a web-based text analysis tool. Upload a set of articles or paste in text (e.g. an abstract) to show word frequency, word clouds etc.

Find subject headings

What are subject headings?
Subject headings are essentially 'tags' that are assigned to articles as they are added to medical databases. Subject headings are used to describe the subject(s) of an article, i.e. what the article is about.

How are subject headings used in literature searching?
Subject headings enable you to find papers that are about your key concepts. In contrast to keywords, subject headings are chosen from an established list and are applied in a consistent manner -- regardless of the language used by authors within individual papers.

Types of subject headings

Different databases often use different subject headings. Subject headings that you may be familiar with are MeSH (Medical Subject Headings) terms used in MEDLINE, Cochrane Library, and PubMed; and Emtree terms used in Embase. It is important to check which subject headings are used in each database that you intend to search.

For example, if one of your main search concepts is ‘complementary medicine’:

In MEDLINE you would use the MeSH term ‘complementary therapies’
In Embase you would use the Emtree term ‘alternative medicine'

What type of subject headings will you need?

Start by viewing our overview of health databases to see which subject headings are used within each database. E.g. if you identified MEDLINE as an appropriate database under Choose database(s) you will need to find relevant MeSH terms.

Health Databases Overview

How to find relevant subject headings

Beginner

Use MeSH tools such as those listed below under 'Tools for finding MeSH terms'.
Open the database(s) that you intend to search, e.g. Embase, and enter one of your keywords or phrases into the main search bar. Click 'Search' and see which subject headings the database suggests may be relevant.

Intermediate / Advanced

Look up known relevant articles in a database such as MEDLINE or Embase and view the 'Complete reference' to see which subject headings have been assigned to each article. Don't use all subject headings assigned to these articles, only those which are relevant to your research question!
Read published systematic reviews on the topic. Many are required to include a copy of their search strategies, or the methodology will sometimes list subject headings used in the search.

Tools for finding MeSH terms

Beginner tools

Use the keywords that you have gathered to search for relevant MeSH terms in the MeSH Database. While viewing a MeSH term, view the 'MeSH Tree Structures' tab to check for other related MeSH terms.

MeSH Database

Intermediate / Advanced tools

The additional tools listed below can extract the MeSH terms which have been applied to specific articles from PubMed. They require you to have already identified one or more papers that are relevant to your research question.

Yale MeSH Analyzer - upload PubMed Identifiers (PMIDs) to create a grid of MeSH terms and author keywords from individual papers.
MeSH on Demand - identifies MeSH terms in an uploaded text (abstract or full text).
PubMed Reminer - provides analysis in a tabular format showing the frequency of terms and MeSH headings from search results.

Combine search terms

Why combine search terms?
You must now combine and group your keywords and subject headings in a meaningful way. This enables the database to make sense of multiple search terms and concepts so that it can provide you with the most relevant results. Essentially, you are telling the database exactly what kind of papers you would like to find.

How to combine search terms

Two small words -- AND and OR -- are the most common and powerful way to combine search terms.

OR - broadens your search by finding papers that contain any of your terms e.g. stroke OR cerebrovascular accident. Use OR to combine similar terms, such as synonyms or spelling variations of the same word (paediatric OR pediatric).

AND - narrows your search by only finding papers that contain both terms e.g. stroke AND aspirin. Use AND to combine different terms or concepts.

How to group search terms

Parentheses (round brackets) are used to group together multiple similar search terms.
For example: (stroke OR cerebrovascular accident OR CVA)

You can use parentheses to create multiple groups, where each group contains terms for a different concept. These groups can then be combined using AND.
For example: (stroke OR cerebrovascular accident OR CVA) AND (aspirin OR acetylsalicylic acid)

Consider pre-built searches

What are pre-built searches?

Pre-built searches are established searches which have been designed to search for specific types of papers. For example, papers of a particular methodological design (e.g. RCTs) or specific health subject area. You can incorporate relevant pre-built searches into your own literature search. Pre-built searches are also referred to as search filters, search hedges, or clinical queries.

Note: Pre-built searches are developed for use in one or more specific databases. I.e. a pre-built search for PubMed cannot be used in Ovid Embase.

Why use pre-built searches?

They are usually developed by experts.
They have often been validated to ensure that they are effective and do not miss relevant papers.
They are a quick and efficient way to search for common medical topics and study designs.

Subject Filters

NSQHS Standards – Live Literature Searches	Topics aligned to the Australian National Safety and Quality Health Service Standards. Easy to use, one click brings up results in PubMed.
Expert Searches - Ovid Medline & Embase	A range of current health topics including Monkeypox, covid, measles, sepsis, health literacy, gender, children, elderly, pregnancy, adverse effects, pharmacovigilance. Also includes study design filters for Medline and Embase. Quick and easy to use, one click opens search in Ovid platform.
Flinders Filters	Subject filters such as Aboriginal and Torres Strait Islander health, dementia, heart failure, lung cancer, stroke etc.
Care Search Palliative Care	Also includes the Heart Failure Search Filter, the Lung Cancer Search Filter, the Dementia Search Filter and the Bereavement Search Filter, for Ovid Medline and for PubMed, as well as the palliAGED Residential Aged Care Search Filter.
Lowitja Institute	Pre-built PubMed searches for Aboriginal and Torres Strait Islander health literature.
Topic-Specific PubMed Queries	Includes subject based filters on topics such as bioethics, cancer, health literacy, toxicology.

Study Design Filters

These pre-built filters can be added to your search to narrow the results to a specific study design, e.g. clinical trials, systematic reviews, meta-analysis, observational, qualitative, health technology assessments etc.

CADTH Search Filters Database	Developed by the Canadian Agency for Drugs and Technologies in Health. Filters for study designs as well as subjects including adverse events, quality of life, economic, guidelines. Different database translations. Quick and easy to use.
The ISSG Search Filter Resource	Developed for research groups within England and Scotland. Filters for study designs as well as subjects including quality of life, guidelines, age, gender, sample size. Different database translation.
PubMed Clinical Queries	Refine PubMed searches based on theory, etiology, diagnosis, prognosis and clinical prediction guide queries. Note: The Systematic Reviews filter is on the main PubMed search results page - under the "Article Type" filter
Expert Searches - Ovid Medline & Embase	Systematic Review, RCT and Observational study design filters for MEDLINE and Embase. Quick and easy to use, one click opens search in Ovid platform.

Considerations when using pre-built search filters

Is it relevant to your research question?
If you are conducting a systematic review, is it relevant to your inclusion criteria?
Is it current? Subject headings and database features can change over time.
Has it been validated?
Was it created by an expert information manager/librarian or research group?

FAQ

Can't find the answer to your question? The Monash Health Library team is here to help -- email us or use our live online chat (Mon-Fri).

Q: Is there a difference between keywords and subject headings?

Yes! Keywords are the natural language terms and phrases used to describe search concepts. Subject headings are "controlled language" words used by databases to ensure that all items relevant to a particular topic will be found. Searching with subject headings is a consistent and precise way to search many databases. However, it is not as flexible as a keyword search because you must know the exact term to use.

Q: Should l use keywords or subject headings in my search?

Both! An effective literature search combines keywords and subject headings for each main concept.

Search Tip: Use keywords as a jumping off point to find corresponding and relevant subject headings for the databases that you are searching on. Remember to keep track of keywords and subject headings you plan to use in your search.

Q: Why do I need to use both keywords and subject headings?

It is important to use both keywords and subject headings in your search because they each have complementary strengths and weaknesses.

If you search using only keywords, you risk missing papers which:
- have not used the exact same words and phrases that you included as keywords in your search. We can't be sure that we have identified all possible synonyms related to a topic or concept, given variation across geographic regions and individual authors/research teams.
If you search using only subject headings, you risk missing papers which:
- are recently published and have not yet been assigned subject headings (this can take weeks or even several months); OR
- have been assigned subject headings that are not included in your search; OR
- may have been assigned an incorrect subject heading. Subject headings are assigned by humans or via the use of AI and regardless, the process is not completely infallible.

Combining keywords and subject headings helps to ensure that your search effectively finds relevant papers.

Q: How can I find studies which have used a certain study design? E.g. only RCTs or only systematic reviews.

You can narrow your results to certain study designs in two ways:

Develop your search based on your research question and then add a pre-built study design filter. For details see the previous step, 3.d) Consider pre-built searches, and its subsection on Study Design Filters. Pre-built filters are generally developed by experts and rigorously tested for effectiveness.
For quick searches, some databases allow you to limit your results to certain study designs. E.g. in Ovid, click "Additional Limits" to access these options.
- In MEDLINE, the "Publication Types" dropdown offers limits for RCTs, systematic reviews, meta-analyses etc.
- In Embase, the "Clinical Trials" dropdown includes RCTs, while the "EBM-Evidence Based Medicine" dropdown includes systematic reviews and meta-analyses.