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Systematic Reviews: Overview

A guide for those who want to do a Systematic Review search strategy mainly in the health sciences field

Systematic Reviews - Overview

This module provides an overview of the steps that should be followed as far as searching for a systematic review.

Why Systematic Reviews

Systematic Review (SR) is a broad review of existing research on a topic that provides synthesis of the evidence from the collected studies to answer a specific question, to guide development of practice guidelines and inform future research.

SRs are gaining in popularity at medical research institutions across US & AUB and it is estimated that 11 SR are published daily, and take about 18 months to do and several people are involved as thousands of articles have to be assessed. The literature search which is the foundation of SR, takes an average of 6 weeks to develop.  

Literature search has to balance between sensitivity & specificity and has to be:

                                comprehensive / efficient / up to date / transparent

So, it is highly recommended to involve an Information Specialist/Medical Librarian as poor search leads to low quality SR; which in turn affects clinical practice adversely; see "engaging medical librarians to improve the quality of review articles".

At The Very Beginning

First it is advisable to read Mayo Clinic Blog: I want to do a systematic review

Then, check if a previous SR already exists or is in-progress using the below resources:

If one already exists, check if it is too old or of poor quality or of a different focus than what you plan.  If SR already exists, look at recommendations for follow-up.

Now, if you decide to do a SR, consider registering the protocol in PROSPERO so it can be peer reviewed and to reduce unnecessary duplication of effort among researchers.

If this is the first time you do a SR, familiarize yourself with:

Covidence: a subscription systematic review collaboration tool from a team of researchers in Australia. Another similar but free tool from Qatar Foundation is Rayyan.  For more information see SR Toolkit.    

Which Topic To Choose

Cochrane Priority Review List

If you want to do a systematic review in your field of specialization, and need a topic that best meets the needs of healthcare and health policy decision makers, we advise you to select a topic of interest from the Cochrane Priority Review List.   This list contains either new titles or reviews requiring updates and is created by the Cochrane Editorial Unit.

Another place to check is AHRQ Funding Priorities.

Writing the Protocol

Any good systematic review begins with a protocol outlining the study methodology. According to the National Institutes of Health (NIH), a protocol serves as a road-map for the review and specifies the objectives, methods, and outcomes of primary interest of the systematic review. The purpose of having a protocol is to promote transparency of methods and reduce bias.

According to University of York the review protocol sets out the methods to be used: decisions about the review question, inclusion criteria, search strategy, study selection, data extraction, quality assessment, data synthesis and plans for dissemination.

If modifications to the protocol are required, these should be clearly documented and justified. Modifications may arise from a clearer understanding of the review question, and should not be made because of an awareness of the results of individual studies.

After you write the protocol, you should register it with PROSPERO, an International Prospective Register of Systematic Reviews. Registration is free and open to anyone undertaking systematic reviews of the effects of interventions and strategies to prevent, diagnose, treat, and monitor health conditions, for which there is a health related outcome.  Cochrane protocols are automatically uploaded onto Prospero.

For more details BioMedCentral provides guidelines on publishing protocols.

Medline/PubMed and Resources Beyond

Usually one starts with Medline (OVID) to develop the search strategy using MeSHes and keywords, and when final, then move to other resources using the same terminology or very similar one.  In addition to health resources, SR topics may require use of non-health resources; such as the ones listed below. To decide which ones to choose depends on the particular question being addressed, along with availability/cost...

Embase / Cochrane Collaboration / CENTRAL / EconLit / Dare / CINAHL / LILACS / IMEMR / Global Index Medicus / POPLINE / PsycInfo / ERIC / AMED / HEED / Campbell Collaboration / Proquest Central / Scopus / Web of Science / Global Health / Health Services  Research from PubMed…

       For more information see Leeds Institute of Health Sciences: Finding Randomised Controlled Trials

If topic of interest involves drugs or devices, contact the company or manufacturer for unpublished studies available in their databases. For drugs also search:

For Medical Devices also seach:

PubMed Search Strategies blog aims to share by posting PubMed search strategies (created by international medical librarians)  in the hope that others will benefit from the work already created.

Broadening Search Sensitivity

To broaden the search strategy to increase number of hits, follow as many of the below tips as applicable:

  • Use related terms (hypertension, antihypertensives…);
  • Use synonyms (cancer, tumor…), such as search Google for [term] synonyms;
  • Use multiple terms/different expressions for same concept (aged, old age…);
  • Use generic and brand names (tylenol, acetaminophen…);
  • Consider variations in punctuation (down’s, downs’…);
  • Consider term variation across different disciplines (bedsores, decupitus…);
  • Use acronyms (AIDS, CIDA…);
  • Consider American & British (paediatrics, pediatrics…);
  • Consider differences in terminology in different countries (SIDS, cot disease…)
  • Consider misspelling mistakes (prostrate cancer, myocardial infraction…)

Convert Medline(OVID) into PubMed

It is recommended that you start searching Medline first, and after finalizing the search strategy with all the MeSH and keywords, the next step is to map that strategy into PubMed commands as shown below:

Types of Systematic Reviews

Systematic Reviews(SR) are high quality, up-to-date reviews written by experts who use rigorous methods to identify all original research studies structured around a focused clearly formulated question.  They appraise / critically evaluate every paper reviewed in a systematic & consistent method. SR make sense of too much sometimes conflicting information, help decision-makers cope with large volume of literature by summarizing reliable research evidence.  

Meta-analyses are systematic reviews that use quantitative (statistical) methods to summarize in a single numerical estimate the results of research.  When results of all included studies are similar enough statistically, they are combined and analyzed as if they were one study, this increases the power of findings that are individually too small to produce reliable results.

Scoping Reviews are the 1st step in doing SR, extensive literature search undertaken to examine previous research activity and to identify previous SR and major clinical trials, disseminate findings, identify research gaps/future needs, and determine value of conducting SR.  Provide an overview of type, extent and quantity of research on a topic, and aim to explore the literature as opposed to answering specific questions; they usually address broad questions so as to help researchers wishing to continue with systematic review, to identify more precise questions, inclusion/exclusion criteria such as interventions, comparators and outcomes of interest.

Living Systematic Review is a new way of updating a systematic review with the purpose of keeping it up-to-date by conducting frequent searches, incorporating new studies into the review, and making the new result available.  This means that the SR will become a continuous process where in real-time new studies are added to the review when they appear.

Umbrella Reviews usually undertaken when there is an already existing large number of published systematic reviews/research syntheses for a particular health topic. These compare/contrast the large number of published systematic reviews and provide an overall examination of a body of information that is available for a given topic.

Narrative Reviews: are selective reviews that collates relevant studies and draw conclusion from them and are considered to be of a low level of evidence.

Integrative Reviews: is very similar to systematic reviews but differs in that it is the only approach that allows for the combination of diverse methodologies (for example, experimental and non-experimental research), and has the potential to play a greater role in evidence-based practice for nursing.

For more information read A typology of reviews: an analysis of 14 review types and associated methodologies also read What kind of systematic review should I conduct... OR just check the table given in that article.

Citation Management Tools

SML subscribes to the below citation management tools that help you to easily collect, manage, organize, remove duplicates and generate citations and bibliographies from the items retrieved from the various databases used:

Others available for free ex. Zotero, Mendeley

“Identifying and Removing Duplicate Records from Systematic Review Searches.” Journal of the Medical Library Association 103(4):184–188, 2015.

You are encouraged to visit the complete ABC guide on how to manage your references from the most important Medical, Nursing, and Public Health databases using Refworks, Endnote Web & Endnote Client.

Contact us if you need help in using any of these.


Transparent Reporting

It is very important that you apply transparent reporting of executed searches.

For databases document:

  • Databases used/ platform/ Dates covered / Date of search;
  • Document full detailed strategy as an appendix at least for one resource, with number of references;
  • Name restrictions such as Language, and filters employed;
  • List qualifications and name of searcher;
  • PRISMA-style flow diagram;
  • Describe search briefly in the methods section.


For non-database provide a brief summary of search method:

  • Internet sources: report the website name, the URL, the date searched, any specific sections searched and the search terms used.
  • Reference lists of selected included studies were scanned for relevant studies.
  • The manufacturing company ….. was contacted for further information (indicate date).
  • Citation searches in WoS or Scopus were carried out for papers citing the recent paper……


Systematic reviews & meta-analyses are essential to summarize evidence relating to efficacy/safety of health-care interventions accurately and reliably, and poor reporting of SR diminishes their value to clinicians, policy makers...

Preferred Reporting Items for Systematic Reviews & Meta-Analyses (PRISMA) is a standardized 27-item checklist and a 4-phase flow diagram, essential for transparent reporting and reproducibility.  Two items from PRISMA apply to the search strategy reporting namely:

PRISMA item 7:

“Studies were identified by searching electronic databases, scanning reference lists of articles and consultation with experts in the field and drug companies. . . . No limits were applied for language and foreign papers were translated. This search was applied to Medline (1966-Present), CancerLit (1975-Present), and adapted for Embase (1980- Present), Science Citation Index Expanded (1981-Present) and Pre-Medline electronic databases. Cochrane and DARE (Database of Abstracts of Reviews of Effectiveness) databases were reviewed. . . . The last search was run on 19 June 2001. In addition, we handsearched contents pages of Journal of Clinical Oncology 2001, European Journal of Cancer 2001 and Bone 2001, together with abstracts printed in these journals 1999-2001. A limited update literature search was performed from 19 June 2001 to 31 December 2003”.

PRISMA Item 8:

In text  “We used the following search terms to search all trials registers and databases: immunoglobulin*; IVIG; sepsis; septic shock; septicaemia; and septicemia . . . ”

In appendix  “Search strategy: MEDLINE (OVID)

  • 01. immunoglobulins/
  • 02. immunoglobulin$.tw.
  • 03.
  • 04. 1 or 2 or 3
  • 05. sepsis/
  • 06.
  • 07. septic shock/
  • 08. septic