search terms in literature review

How to undertake a literature search: a step-by-step guide

Affiliation.

1 Literature Search Specialist, Library and Archive Service, Royal College of Nursing, London.
PMID: 32279549
DOI: 10.12968/bjon.2020.29.7.431

Undertaking a literature search can be a daunting prospect. Breaking the exercise down into smaller steps will make the process more manageable. This article suggests 10 steps that will help readers complete this task, from identifying key concepts to choosing databases for the search and saving the results and search strategy. It discusses each of the steps in a little more detail, with examples and suggestions on where to get help. This structured approach will help readers obtain a more focused set of results and, ultimately, save time and effort.

Keywords: Databases; Literature review; Literature search; Reference management software; Research questions; Search strategy.

Databases, Bibliographic*
Information Storage and Retrieval / methods*
Nursing Research
Review Literature as Topic*

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Key guides for students

Literature Review

How to search effectively.

Find examples of literature reviews
How to write a literature review
Grey literature
GenAI literature search tools

The Literature searching interactive tutorial includes self-paced, guided activities to assist you in developing effective search skills..

1. Identify search words

Analyse your research topic or question.

What are the main ideas?
What concepts or theories have you already covered?
Write down your main ideas, synonyms, related words and phrases.
If you're looking for specific types of research, use these suggested terms: qualitative, quantitative, methodology, review, survey, test, trend (and more).
Be aware of UK and US spelling variations. E.g. organisation OR organization, ageing OR aging.
Interactive Keyword Builder
Identifying effective keywords

2. Connect your search words

Find results with one or more search words.

Use OR between words that mean the same thing.

E.g. adolescent OR teenager

This search will find results with either (or both) of the search words.

Find results with two search words

Use AND between words which represent the main ideas in the question.

E.g. adolescent AND “physical activity”

This will find results with both of the search words.

Exclude search words

Use NOT to exclude words that you don’t want in your search results.

E.g. (adolescent OR teenager) NOT “young adult”

3. Use search tricks

Search for different word endings.

Truncation *

The asterisk symbol * will help you search for different word endings.

E.g. teen* will find results with the words: teen, teens, teenager, teenagers

Specific truncation symbols will vary. Check the 'Help' section of the database you are searching.

Search for common phrases

Phrase searching “...........”

Double quotation marks help you search for common phrases and make your results more relevant.

E.g. “physical activity” will find results with the words physical activity together as a phrase.

Search for spelling variations within related terms

Wildcards ?

Wildcard symbols allow you to search for spelling variations within the same or related terms.

E.g. wom?n will find results with women OR woman

Specific wild card symbols will vary. Check the 'Help' section of the database you are searching.

Search terms within specific ranges of each other

Proximity w/#

Proximity searching allows you to specify where your search terms will appear in relation to each other.

E.g. pain w/10 morphine will search for pain within ten words of morphine

Specific proximity symbols will vary. Check the 'Help' section of the database you are searching.

4. Improve your search results

All library databases are different and you can't always search and refine in the same way. Try to be consistent when transferring your search in the library databases you have chosen.

Narrow and refine your search results by:

year of publication or date range (for recent or historical research)
document or source type (e.g. article, review or book)
subject or keyword (for relevance). Try repeating your search using the 'subject' headings or 'keywords' field to focus your search
searching in particular fields, i.e. citation and abstract. Explore the available dropdown menus to change the fields to be searched.

When searching, remember to:

Adapt your search and keep trying.

Searching for information is a process and you won't always get it right the first time. Improve your results by changing your search and trying again until you're happy with what you have found.

Keep track of your searches

Keeping track of searches saves time as you can rerun them, store references, and set up regular alerts for new research relevant to your topic.

Most library databases allow you to register with a personal account. Look for a 'log in', 'sign in' or 'register' button to get started.

Literature review search tracker (Excel spreadsheet)

Manage your references

There are free and subscription reference management programs available on the web or to download on your computer.

EndNote - The University has a license for EndNote. It is available for all students and staff, although is recommended for postgraduates and academic staff.
Zotero - Free software recommended for undergraduate students.
Previous: How to write a literature review
Next: Where to search when doing a literature review
Last Updated: Oct 21, 2024 11:44 AM
URL: https://uow.libguides.com/literaturereview

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HSL Academic Process
Systematic Reviews
Step 3: Conduct Literature Searches

Systematic Reviews: Step 3: Conduct Literature Searches

Created by health science librarians.

Step 1: Complete Pre-Review Tasks
Step 2: Develop a Protocol

About Step 3: Conduct Literature Searches

Partner with a librarian, systematic searching process, choose a few databases, search with controlled vocabulary and keywords, acknowledge outdated or offensive terminology, helpful tip - building your search, use nesting, boolean operators, and field tags, build your search, translate to other databases and other searching methods, document the search, updating your review.

Searching FAQs
Step 4: Manage Citations
Step 5: Screen Citations
Step 6: Assess Quality of Included Studies
Step 7: Extract Data from Included Studies
Step 8: Write the Review

Check our FAQ's

Email us

Call (919) 962-0800

Make an appointment with a librarian

Request a systematic or scoping review consultation

Search the FAQs

In Step 3, you will design a search strategy to find all of the articles related to your research question. You will:

Define the main concepts of your topic
Choose which databases you want to search
List terms to describe each concept
Add terms from controlled vocabulary like MeSH
Use field tags to tell the database where to search for terms
Combine terms and concepts with Boolean operators AND and OR
Translate your search strategy to match the format standards for each database
Save a copy of your search strategy and details about your search

There are many factors to think about when building a strong search strategy for systematic reviews. Librarians are available to provide support with this step of the process.

Click an item below to see how it applies to Step 3: Conduct Literature Searches.

Reporting your review with PRISMA

For PRISMA, there are specific items you will want to report from your search. For this step, review the PRISMA-S checklist.

PRISMA-S for Searching
Specify all databases, registers, websites, organizations, reference lists, and other sources searched or consulted to identify studies. Specify the date when each source was last searched or consulted. Present the full search strategies for all databases, registers and websites, including any filters and limits used.
For information on how to document database searches and other search methods on your PRISMA flow diagram, visit our FAQs "How do I document database searches on my PRISMA flow diagram?" and "How do I document a grey literature search for my PRISMA flow diagram?"

Managing your review with Covidence

For this step of the review, in Covidence you can:

Document searches in Covidence review settings so all team members can view
Add keywords from your search to be highlighted in green or red while your team screens articles in your review settings

How a librarian can help with Step 3

When designing and conducting literature searches, a librarian can advise you on :

How to create a search strategy with Boolean operators, database-specific syntax, subject headings, and appropriate keywords
How to apply previously published systematic review search strategies to your current search
How to test your search strategy's performance
How to translate a search strategy from one database's preferred structure to another

The goal of a systematic retrieve is to find all results that are relevant to your topic. Because systematic review searches can be quite extensive and retrieve large numbers of results, an important aspect of systematic searching is limiting the number of irrelevant results that need to be screened. Librarians are experts trained in literature searching and systematic review methodology. Ask us a question or partner with a librarian to save time and improve the quality of your review. Our comparison chart detailing two tiers of partnership provides more information on how librarians can collaborate with and contribute to systematic review teams.

Decorative Image: Magnifying glass looking at city lights

Search Process

Use controlled vocabulary, if applicable
Include synonyms/keyword terms
Choose databases, websites, and/or registries to search
Translate to other databases
Search using other methods (e.g. hand searching)
Validate and peer review the search

Databases can be multidisciplinary or subject specific. Choose the best databases for your research question. Databases index various journals, so in order to be comprehensive, it is important to search multiple databases when conducting a systematic review. Consider searching databases with more diverse or global coverage (i.e., Global Index Medicus) when appropriate. A list of frequently used databases is provided below. You can access UNC Libraries' full listing of databases on the HSL website (arranged alphabetically or by subject ).

Generally speaking, when literature searching, you are not searching the full-text article. Instead, you are searching certain citation data fields, like title, abstract, keyword, controlled vocabulary terms, and more. When developing a literature search, a good place to start is to identify searchable concepts of the research question, and then expand by adding other terms to describe those concepts. Read below for more information and examples on how to develop a literature search, as well as find tips and tricks for developing more comprehensive searches.

Identify search concepts and terms for each

Start by identifying the main concepts of your research question. If unsure, try using a question framework to help identify the main searchable concepts. PICO is one example of a question framework and is used specifically for clinical questions. If your research question doesn't fit into the PICO model well, view other examples of question frameworks and try another!

View our example in PICO format

Question: for patients 65 years and older, does an influenza vaccine reduce the future risk of pneumonia, controlled vocabulary.

Controlled vocabulary is a set of terminology assigned to citations to describe the content of each reference. Searching with controlled vocabulary can improve the relevancy of search results. Many databases assign controlled vocabulary terms to citations, but their naming schema is often specific to each database. For example, the controlled vocabulary system searchable via PubMed is MeSH, or Medical Subject Headings. More information on searching MeSH can be found on the HSL PubMed Ten Tips Legacy Guide .

Note: Controlled vocabulary may be outdated, and some databases allow users to submit requests to update terminology.

View Controlled Vocabulary for our example PICO

As mentioned above, databases with controlled vocabulary often use their own unique system. A listing of controlled vocabulary systems by database is shown below.

Keyword Terms

Not all citations are indexed with controlled vocabulary terms, however, so it is important to combine controlled vocabulary searches with keyword, or text word, searches.

Authors often write about the same topic in varied ways and it is important to add these terms to your search in order to capture most of the literature. For example, consider these elements when developing a list of keyword terms for each concept:

American versus British spelling
hyphenated terms
quality of life
satisfaction
vaccination
influenza vaccination

There are several resources to consider when searching for synonyms. Scan the results of preliminary searches to identify additional terms. Look for synonyms, word variations, and other possibilities in Wikipedia, other encyclopedias or dictionaries, and databases. For example, PubChem lists additional drug names and chemical compounds.

Display Controlled Vocabulary and Keywords for our example PICO

Combining controlled vocabulary and text words in PubMed would look like this:

"Influenza Vaccines"[Mesh] OR "influenza vaccine" OR "influenza vaccines" OR "flu vaccine" OR "flu vaccines" OR "flu shot" OR "flu shots" OR "influenza virus vaccine" OR "influenza virus vaccines"

Social and cultural norms have been rapidly changing around the world. This has led to changes in the vocabulary used, such as when describing people or populations. Library and research terminology changes more slowly, and therefore can be considered outdated, unacceptable, or overly clinical for use in conversation or writing.

For our example with people 65 years and older, APA Style Guidelines recommend that researchers use terms like “older adults” and “older persons” and forgo terms like “senior citizens” and “elderly” that connote stereotypes. While these are current recommendations, researchers will recognize that terms like “elderly” have previously been used in the literature. Therefore, removing these terms from the search strategy may result in missed relevant articles.

Research teams need to discuss current and outdated terminology and decide which terms to include in the search to be as comprehensive as possible. The research team or a librarian can search for currently preferred terms in glossaries, dictionaries, published guidelines, and governmental or organizational websites. The University of Michigan Library provides suggested wording to use in the methods section when antiquated, non-standard, exclusionary, or potentially offensive terms are included in the search.

Check the methods sections or supplementary materials of published systematic reviews for search strategies to see what terminology they used. This can help inform your search strategy by using MeSH terms or keywords you may not have thought of. However, be aware that search strategies will differ in their comprehensiveness.

You can also run a preliminary search for your topic, sort the results by Relevance or Best Match, and skim through titles and abstracts to identify terminology from relevant articles that you should include in your search strategy.

Nesting is a term that describes organizing search terms inside parentheses. This is important because, just like their function in math, commands inside a set of parentheses occur first. Parentheses let the database know in which order terms should be combined.

Always combine terms for a single concept inside a parentheses set. For example:

( "Influenza Vaccines"[Mesh] OR "influenza vaccine" OR "influenza vaccines" OR "flu vaccine" OR "flu vaccines" OR "flu shot" OR "flu shots" OR "influenza virus vaccine" OR "influenza virus vaccines" )

Additionally, you may nest a subset of terms for a concept inside a larger parentheses set, as seen below. Pay careful attention to the number of parenthesis sets and ensure they are matched, meaning for every open parentheses you also have a closed one.

Boolean operators

Boolean operators are used to combine terms in literature searches. Searches are typically organized using the Boolean operators OR or AND. OR is used to combine search terms for the same concept (i.e., influenza vaccine). AND is used to combine different concepts (i.e., influenza vaccine AND older adults AND pneumonia). An example of how Boolean operators can affect search retrieval is shown below. Using AND to combine the three concepts will only retrieve results where all are present. Using OR to combine the concepts will retrieve results that use all separately or together. It is important to note that, generally speaking, when you are performing a literature search you are only searching the title, abstract, keywords and other citation data. You are not searching the full-text of the articles.

The last major element to consider when building systematic literature searches are field tags. Field tags tell the database exactly where to search. For example, you can use a field tag to tell a database to search for a term in just the title, the title and abstract, and more. Just like with controlled vocabulary, field tag commands are different for every database.

If you do not manually apply field tags to your search, most databases will automatically search in a set of citation data points. Databases may also overwrite your search with algorithms if you do not apply field tags. For systematic review searching, best practice is to apply field tags to each term for reproducibility.

For example:

("Influenza Vaccines"[Mesh] OR "influenza vaccine"[tw] OR "influenza vaccines"[tw] OR "flu vaccine"[tw] OR "flu vaccines"[tw] OR "flu shot"[tw] OR "flu shots"[tw] OR "influenza virus vaccine"[tw] OR "influenza virus vaccines"[tw] OR ((flu[tw] OR influenza[tw]) AND (vaccine[tw] OR vaccines[tw] OR vaccination[tw] OR immunization[tw])))

View field tags for several health databases

For more information about how to use a variety of databases, check out our guides on searching.

Searching PubMed guide Guide to searching Medline via the PubMed database
Searching Embase guide Guide to searching Embase via embase.com
Searching Scopus guide Guide to searching Scopus via scopus.com
Searching EBSCO Databases guide Guide to searching CINAHL, PsycInfo, Global Health, & other databases via EBSCO

Combining search elements together

Organizational structure of literature searches is very important. Specifically, how terms are grouped (or nested) and combined with Boolean operators will drastically impact search results. These commands tell databases exactly how to combine terms together, and if done incorrectly or inefficiently, search results returned may be too broad or irrelevant.

For example, in PubMed:

(influenza OR flu) AND vaccine is a properly combined search and it produces around 50,000 results.

influenza OR flu AND vaccine is not properly combined. Databases may read it as everything about influenza OR everything about (flu AND vaccine), which would produce more results than needed.

We recommend one or more of the following:

put all your synonyms together inside a set of parentheses, then put AND between the closing parenthesis of one set and the opening parenthesis of the next set
use a separate search box for each set of synonyms
run each set of synonyms as a separate search, and then combine all your searches
ask a librarian if your search produces too many or too few results

View the proper way to combine MeSH terms and Keywords for our example PICO

Question: for patients 65 years and older, does an influenza vaccine reduce the future risk of pneumonia , translating search strategies to other databases.

Databases often use their own set of terminology and syntax. When searching multiple databases, you need to adjust the search slightly to retrieve comparable results. Our sections on Controlled Vocabulary and Field Tags have information on how to build searches in different databases. Resources to help with this process are listed below.

Polyglot search A tool to translate a PubMed or Ovid search to other databases
Search Translation Resources (Cornell) A listing of resources for search translation from Cornell University
Advanced Searching Techniques (King's College London) A collection of advanced searching techniques from King's College London

Other searching methods

Hand searching.

Literature searches can be supplemented by hand searching. One of the most popular ways this is done with systematic reviews is by searching the reference list and citing articles of studies included in the review. Another method is manually browsing key journals in your field to make sure no relevant articles were missed. Other sources that may be considered for hand searching include: clinical trial registries, white papers and other reports, pharmaceutical or other corporate reports, conference proceedings, theses and dissertations, or professional association guidelines.

Searching grey literature

Grey literature typically refers to literature not published in a traditional manner and often not retrievable through large databases and other popular resources. Grey literature should be searched for inclusion in systematic reviews in order to reduce bias and increase thoroughness. There are several databases specific to grey literature that can be searched.

Open Grey Grey literature for Europe
OAIster A union catalog of millions of records representing open access resources from collections worldwide
Grey Matters: a practical tool for searching health-related grey literature (CADTH) From CADTH, the Canadian Agency for Drugs and Technologies in Health, Grey Matters is a practical tool for searching health-related grey literature. The MS Word document covers a grey literature checklist, including national and international health technology assessment (HTA) web sites, drug and device regulatory agencies, clinical trial registries, health economics resources, Canadian health prevalence or incidence databases, and drug formulary web sites.
Duke Medical Center Library: Searching for Grey Literature A good online compilation of resources by the Duke Medical Center Library.

Systematic review quality is highly dependent on the literature search(es) used to identify studies. To follow best practices for reporting search strategies, as well as increase reproducibility and transparency, document various elements of the literature search for your review. To make this process more clear, a statement and checklist for reporting literature searches has been developed and and can be found below.

PRISMA-S: Reporting Literature Searches in Systematic Reviews
Section 4.5 Cochrane Handbook - Documenting and reporting the search process

At a minimum, document and report certain elements, such as databases searched, including name (i.e., Scopus) and platform (i.e. Elsevier), websites, registries, and grey literature searched. In addition, this also may include citation searching and reaching out to experts in the field. Search strategies used in each database or source should be documented, along with any filters or limits, and dates searched. If a search has been updated or was built upon previous work, that should be noted as well. It is also helpful to document which search terms have been tested and decisions made for term inclusion or exclusion by the team. Last, any peer review process should be stated as well as the total number of records identified from each source and how deduplication was handled.

If you have a librarian on your team who is creating and running the searches, they will handle the search documentation.

You can document search strategies in word processing software you are familiar with like Microsoft Word or Excel, or Google Docs or Sheets. A template, and separate example file, is provided below for convenience.

Search Strategy Documentation Template
Search Strategy Documentation Example

*Some databases like PubMed are being continually updated with new technology and algorithms. This means that searches may retrieve different results than when originally run, even with the same filters, date limits, etc.

When you decide to update a systematic review search, there are two ways of identifying new articles:

1. rerun the original search strategy without any changes. .

Rerun the original search strategy without making any changes. Import the results into your citation manager, and remove all articles duplicated from the original set of search results.

2. Rerun the original search strategy and add an entry date filter.

Rerun the original search strategy and add a date filter for when the article was added to the database ( not the publication date). An entry date filter will find any articles added to the results since you last ran the search, unlike a publication date filter, which would only find more recent articles.

Some examples of entry date filters for articles entered since December 31, 2021 are:

PubMed: AND ("2021/12/31"[EDAT] : "3000"[EDAT])
Embase: AND [31-12-2021]/sd
CINAHL: AND EM 20211231-20231231
PsycInfo: AND RD 20211231-20231231
Scopus: AND LOAD-DATE AFT 20211231

Your PRISMA flow diagram

For more information about updating the PRISMA flow diagram for your systematic review, see the information on filling out a PRISMA flow diagram for review updates on the Step 8: Write the Review page of the guide.

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Next: Step 4: Manage Citations >>
Last Updated: Nov 6, 2024 9:29 AM
URL: https://guides.lib.unc.edu/systematic-reviews