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Systematic Reviews, a Guide: How to Search

Search Terms

The terms you use is one of the single most important aspects of searching for literature. It is crucial to capture as many ways to express an idea, concept or thing so as to capture as much relevant literature available.

You do not have to know all the ways an idea is expressed when you first begin, especially if a concept is more qualitative than quantitative. As you search, you will begin to see synonyms and other terms other authors use to express similar things.

Where to find terms

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 is one of the few that does not have a controlled vocabulary.

It is important to search both keywords and the database's controlled vocabulary (where applicable) to catch as many results as possible. 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 terms.

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.

Citation Chaining

"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:

Google Scholar

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.

Web of Science

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.]

Yale MeSH Analyzer

Yale MeSH Analyzer

The Yale MeSH Analyzer tool will create an analysis grid of one or more articles to retrieve the MeSH as well as author-supplied keywords. An excellent tool to compare relevant articles' MeSH and keywords and a way to discover other terms to use when searching or help find gaps in search strategies. 

From the website:

"A MeSH analysis grid can help identify the problems in your search strategy by presenting the ways articles are indexed in the MEDLINE database in an easy-to-scan tabular format. Typically, each column in the grid represents an article, with identifying information of the article at the top of the column, such as the PMID, the author, and the year of publication. The Medical Subject Headings are sorted and grouped alphabetically for ease of scanning. Librarians can then easily scan the grid and identify appropriate MesH terms, term variants, indexing consistency, and the reasons why some articles are retrieved and others are not. This inevitably leads to fresh iterations of the search strategy to include missing important terms."

Saving Searches

It's very important to save searches in every database searched, either by saving them within your personal account in the database (for example, in PubMed, you can use My NCBI), saving them to a document on your computer, or printing them off. You will use these later when writing up the methods or sharing with those who will write the methods, such as other researchers or the librarian with whom you worked.

Boolean Operators

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

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

Database Filters & Limits

These can be helpful to winnow down results.

Some argue, however, that you will want as many results as possible that you will then manually, based on your exclusion/inclusion criteria, sift through and choose appropriate articles to examine later.

Whatever you do, one thing to keep in mind is that citations are not always indexed properly with the appropriate limits/filters.  And if you do use filters and limits in your searches, remember to include them in your methodology.

Truncation & Wildcards

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: 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 $, though always best to check the database documentation.

Example: behavio$r captures both the American spelling, behavior, and the British spelling, behaviour