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Systematic Reviews & Evidence Synthesis

About Step 3: Conduct Literature Searches

Step 3: Conduct Literature Searches
Average time (in hours) to complete

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

  1. Define the main concepts of your domain of study
  2. Choose which databases to search
  3. List terms to describe each concept using controlled vocabulary like MeSH
  4. Use field tags to tell the database where to search for terms
  5. Combine terms and concepts with Boolean operators AND and OR
  6. Translate your search strategy for each database
  7. Enter your search strategy details and results into a research log

How (AND WHY) a librarian SHOULD help with this step

ZSR strongly advises that you use a librarian's support for this step! Since the goal of a SR is to find every article ever published on your topic, SR 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. We can save you time and help to improve the quality of your review. Visit ZSR's Partnership Options page to see the varying levels of services we provide for Evidence Synthesis (or review type) projects. 

ZSR can help you: 

  • Create your search strategy with Boolean operators, indexed terms (like MeSH), keywords, and tags
  • Apply previously used search strategies or hedges into your current search
  • Test your search strategy's performance
  • Translate your search strategy across all databases being used in your project

Click HERE to contact us for SR support!

The Systematic Searching Process

The Search Process 

Since the goal of a SR is to find every article ever published on your topic, SR searches can be quite extensive and retrieve large numbers of results. The search process includes the following tasks: 

  • Identifying search terms for each component of your research question
    • Use controlled vocabulary per database (like MeSH terms)
    • Include synonyms / keyword terms
  • Choosing appropriate databases, websites, and/or registries to search
  • Constructing the search strategy
    • Using nesting, Boolean operators, and field tags
    • Translating to other databases
    • Determining other methods of search (e.g. hand searching)
  • Validating the search through librarian or peer review
  • Documenting search iterations

How is a systematic review different from a typical literature review? 

A systematic review is a form of a literature review, but the SR's methodology is much more rigorous with an attempt to minimize bias. Check out the main differences list here...

Literature Review Systematic Review
Focus Broad topic is general overview
Specific research question based on framework(s)
Methodology Flexible Systematic, comprehensive, transparent approach to searching, selecting, assessing selected studies
Replicability Not shared with reader Full search strategy should be published and available for reader replication
Bias  Susceptible to author bias Utilize tools & checklists to actively minimize (methodology) and assess (in selected studies)
Synthesis Narrative Reported using tabular format along with a narrative review (incorporates ROB judgements)

Another way to look at this difference is to think of a missing puzzle piece. 

The goal of a typical literature review is to find the gap (or the missing piece) of evidence available in the literature. 

The goal of a systematic review is to fill the gap (or find the missing piece) by synthesizing ALL the evidence available in the literature that can answer a specific research question.  

Choosing databases

It is important to choose the best and appropriate number of databases for your research question. Consider these few things when choosing:

  • Different databases index different journals, so multiple databases should be searched in order to conduct the comprehensive search necessary for SR projects
  • Databases can be multidisciplinary or subject specific; using both types to ensure diverse and global coverage is recommended

A list of frequently used databases for biomedical SR's is provided below. You can access ZSR's full list of databases HERE.

Want to learn more about sources other than databases? Visit ZSR's Building a Comprehensive & Exhaustive Search Page

Choosing search terms

What's the BIG DEAL?!

When you conduct searches in library databases, you are searching citation data (like title, abstract, keyword, controlled vocabulary terms) - NOT the full text article. Therefore, when crafting your search strategy, you should: 

  1. Identify searchable concepts of your research question 
  2. Expand those by adding other terms to describe those concepts

Select the tabs in this sections to learn more on developing a literature search - tips and tricks included!

For more searching tips & tricks, visit ZSR's Building a Comprehensive & Exhaustive Search Page

Identify Search Terms

Start by identifying the main concepts of your research question by using a question framework. 

See our PICO example below. 

Research Question: In adults with sickle cell disease (SCD), what is the efficacy of hydroxyurea as compared to placebo in reducing vaso-occlusive crises?

Concept Example
P - (Patient / Population adults with SCD
I - Intervention hydroxyurea
C - Comparator placebo
O - Outcome vaso-occlusive crises

For more searching tips & tricks, visit ZSR's Building a Comprehensive & Exhaustive Search Page

Controlled Vocabulary

Controlled vocabulary is a set of terminology assigned to citations to describe the content of each reference. A couple of items to note here: 

  • 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: Pubmed - MeSH, CINHAL - CINHAL subject headings, Embase - Emtree)

Note: Controlled vocabularies are typically updated by database managers. Typically users can submit requests to update terminology (especially when new terms are used to describe populations, procedures, diagnoses, etc.)

For more searching tips & tricks, visit ZSR's Building a Comprehensive & Exhaustive Search Page

Keyword Terms

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

Authors write about the same topic in varied ways so adding varied terms to your search can help capture most of the literature.

Here are some examples:

Terms with similar meanings flu / influenza, heart attack / myocardial infraction
Terms with different spellings Hyphenations, American vs. British spellings
Acronyms MS / Multiple Sclerosis, BMI / Body Mass Index
Concepts described inconsistently Patient satisfaction, quality of life
Broad versus specific terms vaccine / flu vaccine, cancer / breast cancer

There are several resources to help you find additional terms:

  • Scan the results of preliminary searches
  • Check out Wikipedia, wordhippo, or other encyclopedias for synonyms, word variations

For more searching tips & tricks, visit ZSR's Building a Comprehensive & Exhaustive Search Page

BE AWARE: Outdated / Offensive Terms

Social and cultural norms rapidly change - including how the literature describes people or populations. However, library and research terminology can't change at the same pace; therefore that terminology can be considered outdated, unacceptable, or too clinical for use in conversation or writing.

For instance, MeSH terms have evolved over the years to reflect more current and inclusive terminology. A few examples include: 

  • African Continental Ancestry Group was replaced with Blacks.
  • American Natives was replaced with American Indians or Alaska Natives
  • Asian Continental Ancestry Group was replaced with Asians.
  • Continental Population Groups was replaced with Racial Groups
  • Ethnic Groups was replaced with Ethnicity
  • European Continental Ancestry Group was replaced with Whites.
  • Hispanic Americans was replaced with Hispanic or Latino
  • Oceanic Ancestry Group was replaced with Native Hawaiian or Other Pacific Islander. 

Although the National Library of Medicine strive to stay current with terminology, MeSH terms are only updated once per year; therefore including previously used terms (although outdated) in your search may result in more relevant articles returned. 

Discuss current and outdated terminology and decide which terms to include in the search so you can create as comprehensive of a search as possible. ZSR can help your team search for currently preferred terms. 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.

For more searching tips & tricks, visit ZSR's Building a Comprehensive & Exhaustive Search Page