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Literature reviews: Systematic reviews

“A systematic review strives to identify and comprehensively track down all the available literature on a topic, while describing a clear, comprehensive methodology.”

Helen Aveyard, Doing A Literature Review In Health And Social Care: A Practical Guide

This guide offers support and useful links for completing a systematic review. A high quality systematic review is typically conducted by a team of researchers over a long time period. This guide is aimed at individual researchers searching systematically but over a shorter time span.

What is a systematic review?

A systematic review:

attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a specific research question.

(Definition from Cochrane Collaboration

They need to be reproducible, transparent and the methodology used to collect the research has to be consistent in order to reduce misinterpretation and misrepresentation of the data.

High quality systematic reviews usually involve a minimum of two people working as part of a research team and can typically take a minimum of a year to complete. Cochrane Collaboration reviews, for instance, cannot be produced by individuals as the selection of studies for eligibility and data extraction has to be performed by at least two people independently.

The review should be based on a peer-reviewed protocol (plan) which describes the review question, a rationale for the proposed methods and details of how different types of studies will be located, appraised and synthesised.

At university, undergraduate students in health sciences are often asked to undertake a systematic-style review. They should follow the same basic process as a full review with the acknowledgment that this will not be as rigorous or as comprehensive as those needed for a Cochrane Collaboration review.

Simple/traditional literature review vs systematic review

Systematic reviews are considered to be a higher quality than a traditional literature review: more comprehensive and less biased. They are characterised by being methodical, comprehensive, transparent and replicable. They involve:

  • a systematic search process to locate all relevant published and unpublished work that addresses a clear focused research question.
  • a systematic presentation and synthesis of the results of that search.

The systematic methodology and presentation aim to minimise subjectivity and bias. The criteria for inclusion and exclusion are also explicitly stated and consistently implemented. Whereas a traditional literature review may offer an overview on a general topic, a systematic review will aim to answer a clear question and make recommendations for practice.

Steps and processes involved in a systematic review

Consider whether a systematic review is necessary and whether you have the time and resources to conduct one. You need to establish whether one has been done on your topic already, or is about to be conducted. Protocols of new reviews in health sciences will be registered on PROSPERO. You can also check databases such as the Cochrane Library and Campbell Collaboration to establish if any have been published.

There are five key steps in producing a systematic literature review:

Step 1 - Formulate your research question.

Step 2 - Identify your search terms and conduct your searches.

Step 3 - Assess the quality of the studies.

Step 4 - Summarise the evidence.

Step 5 - Interpret the findings.

Structuring and presenting your review

There is no right way of doing this as what you cover and how you organise it should be directed by the goals you have set for the review. However, there are some general principles and it is recommended you adhere to best practice guidelines for conducting and reporting the review such as the PRISMA checklist which can service as an outline for your review. There are 27 items on the checklist so it is very comprehensive.

It's also worth looking at several reviews published in top journals in your field and using these as templates for formatting and content.

Generally you would expect to see:

  • Title
  • Abstract
  • Introduction
  • Methods
  • Results
  • Discussion