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Gerstein Science Information Centre

Searching the Literature: A Guide to Comprehensive Searching in the Health Sciences

Students and researchers in the health sciences are often required to conduct comprehensive searches of the literature. Follow the steps in this guide to learn how this process works.

Precision vs. Sensitivity - Key to Effective Searching

When searching for literature, it's important to ask yourself: Do you want to do a PRECISE search of the literature or a SENSITIVE search of the literature?


This guide focuses on how to develop a sensitive, or comprehensive, search. 


A precise search:

  • PRO: captures some relevant literature
  • PRO: captures fewer irrelevant results, less time filtering and screening
  • CON: risk of missing relevant literature is high

A sensitive search: 

  • PRO: captures most relevant literature
  • PRO: risk of missing relevant literature is low
  • CON: captures higher proportion of irrelevant literature, more time filtering and screening


As demonstrated by the graphic below, it is impossible to achieve high precision and high sensitivity at the same time.


large pink circle with predominantly pink dots and some green; inside, a green circle with very clustered green dots. Green represents a precise search; pink represents a sensitive search.                     

Sensitivity and precision can be calculated using the following formulas:

Sensitivity: # of relevant reports identified / total # of relevant reports in existence

Precision: # of relevant reports identified / total # of reports identified

Will you Search for Sensitivity or Precision?

There's a logic to searching: 

  • As sensitivity goes up, precision goes down ; THEREFORE,
  • A sensitive search must retrieve a high proportion of irrelevant results; THEREFORE, 
  • If your search results are mostly-to-all relevant, it's highly likely you're missing things
It's your job as a searcher to find the right balance between sensitivity and precision. 


This balance is determined by: 

  • your question OR
  • your objectives
Using the table below, what kind of search will you need to develop? 

    Precise search questions: 

    • can be answered with high degree of certainty
    • concepts in question are clear and easily defined
    • ex. What is the recommend daily dose of regular-strength tylenol for a child with fever? 

    Sensitive search questions: 

    • requires gathering many sources of evidence
    • concepts within the question are difficult to define and operationalize
    • ex. What is the best way to increase frequency of hand hygiene practices in a busy, urban emergency department? 

    Precise search objectives, for example: 

    • I only need a few, recent articles on the use of simulation in education to improve teamwork, in order to stimulate discussion in class
    • I need to find a highly-cited RCT or systematic review on the effectiveness of acetaminophen for fever in children 

    Sensitive search objectives, for example: 

    • I'm conducting a review of the literature
    • I'm preparing a protocol for a primary research study and I need to find examples of a particular methodology in the published literature
    • I'm nervous about missing studies 

Find the Right Balance

Now that you've identified the kind of search you want to conduct, think about ways to move your results in either direction until you find the right balance. 

Tips to increase sensitivity: 

  • refine question or objective
  • conduct a structured search of the literature using subject headings and textwords
  • remove concept from your search
    • instead of CANCER and CHEMOTHERAPY and NAUSEA --> search CHEMOTHERAPY and NAUSEA instead
  • search more synonyms for each concept in your question (find the outliers!)
    • instead of CHEMOTHERAPY and NAUSEA --> search (chemotherapy OR alemtuzumab OR cisplatin OR Hexalen ) AND (nausea OR vomiting OR emesis)
  • search more than 1 database 

Tips to increase precision: 

  • refine question or objective
  • add a concept to your search, or combine two concepts into one
    • instead of TYLENOL and FEVER --> search TYLENOL and FEVER and RANDOMIZED 
  • restrict search words to title, title/abstract, or author-provided keywords
  • use tools of the database to restrict search results to only those where your concept is the MAJOR SUBJECT of the article
  • use study filters, date limits, or clinical queries to restrict results of the search
  • use different sort options to force more relevant or higher cited articles to the top of your results (in some databases)
  • search a distilled information resource, such as Dynamed Plus or LexiComp, instead of a database

This work is openly licensed via CC BY-NC-SA 4.0For information on this guide contact Erica Nekolaichuk, Faculty Liaison & Instruction Librarian at the Gerstein Science Information Centre.