A literature search is a thorough and organized search used to find key literature on a certain subject or topic. In order to properly conduct a literature search, you need to be able to look through your available resources in an efficient manner. This guide gives a brief overview of different techniques used in a literature search.
Searching for literature can be a daunting task. Below are several tips and strategies to consider and use when searching for literature:
The terms you use is one of the single most important aspects of searching for literature.
Where to find terms
You do not have to know all the ways an idea is expressed when you first begin. As you search, you will begin to see synonyms and other terms other authors use to express similar things.
Many electronic databases have a special vocabulary that indexers use to index citations. MEDLINE (found in PubMed) uses MeSH (Medical Subject Headings), CINAHL uses its own Subject Headings, to name two. Always seek out the thesaurus or controlled vocabulary of each database you are using if they have one. Web of Science and Scopus are two of the few that do not have a controlled vocabulary.
It is not always necessary to search both keywords and the database's controlled vocabulary (where applicable), but doing can catch as many results as possible and it is important to do so when conducting a larger search like a systematic review. For example, searching with MeSH alone will only capture results indexed with MeSH and may miss anything not yet indexed, as is the case with the most recently added citations, while keywords will capture anything not indexed with MeSH term.
By searching in the database's controlled vocabulary, you can find other terms to use.
For example, we might say heart attack. In MeSH, the term is myocardial infarction.
Phrases
When searching for phrases, it is important to use quotation marks, which are used in most databases to denote phrases, around the phrase. Example: "quality of life"
Doing this tells the database to keep those words together in the order given. Without the quotation marks, databases may look for the terms separately. Some databases must recognize a phrase first in order to search for said phrase, such as PubMed. (If PubMed does not recognize a phrase, it will give an error message and search for the terms separately.)
There are three Boolean operators that are used to connect terms and tell databases how and what to search for: AND, OR, NOT.
AND is to combine terms, usually unlike terms/concepts. AND narrows a search. Example: social media AND teenagers
OR is typically used with synonyms and similar terms. OR broadens a search. Example: teenagers OR adolescents
NOT is used to exclude something. Example: teenagers NOT bullying
(Note: use NOT with caution as it can eliminate results that could be relevant. For example, some studies include more than one population and running a search with the NOT operator to eliminate one of those populations will eliminate those studies that include both the desired and undesired populations -- studies that could have potentially relevant information.)
We use parentheses to help group parts of the search query, especially when we have several parts, and to tell the database the order of the query. Think about the search query as a mathematical equation.
All put together, they look like this:
social media AND (teenager OR adolescent) NOT bullying
Truncation allows you to find different endings to a word. The symbol in many databases is: *
Example: teenage* captures teenager, teenagers, teenaged.
Be careful not to truncate too far into the word. For example, say you want endings of carbohydrate. Truncating to car* will capture car, cardiology, carbohydrate, caramel, carabidae, carassius, and thousands more words.
carbohydrat* would be a better way to truncate.
Wildcards are symbols used within a word to represent a letter for a variation on spelling. While not every database uses them anymore, for those that do, the symbol is often ? or # or $, though always best to check the database documentation.
Example: behavio$r captures both the American spelling, behavior, and the British spelling, behaviour
"Citation chaining" is a way of searching both backward and forward in the literature to find more relevant papers using a single paper as a starting point. Such a search, starting with one paper, creates a "chain" of references linked backward and forward from the original paper.
How does it work?
When you have a relevant paper, see the references it cites (in the cited works/references/bibliography). From those, there may be other relevant papers that those papers cite that may be of use. This is going backward in the chain. One can go back many times in the literature.
To go forward in the chain, see what other papers cited the original paper.
To do that, here are two recommended resources:
In Google Scholar, search for the original paper. In the results, look for the "Cited By [# results]" link just below the link to the paper.
In Web of Science, use the Cited Reference Search.
[Note: there will be some overlap between the two, but the results will not always be the same. Web of Science only shows what is indexed in Web of Science, whereas Google Scholar searches all over.]