Literature Search Basics

KEY POINTS

• A search strategy includes a combination of keywords, subject headings, and limiters (language, date, publication type, etc.)
• A search strategy should be planned out and practiced before executing the final search in a database.
• A search strategy and search results should be documented throughout the searching process.

What is a search strategy?

A search strategy is an organized combination of keywords, phrases, subject headings, and limiters used to search a database.

Your search strategy will include:

• keywords 
• boolean operators
• variations of search terms (synonyms, suffixes)
• subject headings 

Your search strategy may include:

• truncation (where applicable)
• phrases (where applicable)
• limiters (date, language, age, publication type, etc.)

A search strategy usually requires several iterations. You will need to test the strategy along the way to ensure that you are finding relevant articles. It's also a good idea to review your search strategy with your co-authors. They may have ideas about terms or concepts you may have missed.

Additionally, each database you search is developed differently. You will need to adjust your strategy for each database your search.  For instance, Embase is a European database, many of the medical terms are slightly different than those used in MEDLINE and PubMed.

Choose search terms

Start by writing down as many terms as you can think of that relate to your question. You might try cited reference searching to find a few good articles that you can review for relevant terms.

Remember than most terms or  concepts can be expressed in different ways.  A few things to consider:

• synonyms: "cancer" may be referred to as "neoplasms", "tumors", or "malignancy"
• abbreviations: spell out the word instead of abbreviating
• suffixes
• generic vs. trade names of drugs

Search for the exact phrase

If you want words to appear next to each other in an exact phrase, use quotation marks, eg “self-esteem”.

Phrase searching decreases the number of results you get. Most databases allow you to search for phrases, but check the database guide if you are unsure.

Truncation and wildcards

Many databases use an asterisk (*) as their truncation symbol to find various word endings like singulars and plurals. Check the database help section if you are not sure which symbol to use. 

"Therap*"

retrieves: therapy, therapies, therapist or therapists.

Use a wildcard (?) to find different spellings like British and American spellings.

"Behavio?r" retrieves behaviour and behavior.

Searching with subject headings

Database subject headings are controlled vocabulary terms that a database uses to describe what an article is about.

Using appropriate subject headings enhances your search and will help you to find more results on your topic. This is because subject headings find articles according to their subject, even if the article does not use your chosen key words.

You should combine both subject headings and keywords in your search strategy for each of the concepts you identify. This is particularly important if you are undertaking a systematic review or an in-depth piece of work

Subject headings may vary between databases, so you need to investigate each database separately to find the subject headings they use. For example, for MEDLINE you can use MeSH (Medical Subject Headings) and for Embase you can use the EMTREE thesaurus.

SEARCH TIP: In Ovid databases, search for a known key paper by title, select the "complete reference" button to see which subject headings the database indexers have given that article, and consider adding relevant ones to your own search strategy.

Use Boolean logic to combine search terms

Boolean operators (AND, OR and NOT) allow you to try different combinations of search terms or subject headings.

Databases often show Boolean operators as buttons or drop-down menus that you can click to combine your search terms or results.

The main Boolean operators are:

• OR
• AND
• NOT

OR is used to find articles that mention either of the topics you search for.

AND is used to find articles that mention both of the searched topics.

NOT excludes a search term or concept. It should be used with caution as you may inadvertently exclude relevant references.

For example, searching for “self-esteem NOT eating disorders” finds articles that mention self-esteem but removes any articles that mention eating disorders.

Adjacency searching 

Use adjacency operators to search by phrase or with two or more words in relation to one another. Adjacency searching commands differ among databases. Check the database help section if you are not sure which searching commands to use. 

In Ovid Medline

"breast ADJ3 cancer" finds the word breast within three words of cancer, in any order.

This includes breast cancer or cancer of the breast.

Cited Reference Searching

Cited reference searching is a method to find articles that have been cited by other publications. 

Use cited reference searching to:

• find keywords or terms you may need to include in your search strategy
• find pivotal papers the same or similar subject area
• find pivotal authors in the same or similar subject area
• track how a topic has developed over time

Cited reference searching is available through these tools:

• Web of Science
• Scopus
• GoogleScholar