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Systematic reviews: What is a systematic review?

A quick guide to introduce you to systematic reviews

Quick guide

A systematic review is a summary of all of the literature on a particular topic, that meets pre-defined eligibility criteria.

The Cochrane Collaboration definition:

"A systematic review summarises the results of available carefully designed healthcare studies (controlled trials) and provides a high level of evidence on the effectiveness of healthcare interventions. Judgments may be made about the evidence and inform recommendations for healthcare.

These reviews are complicated and depend largely on what clinical trials are available, how they were carried out (the quality of the trials) and the health outcomes that were measured. Review authors often pool numerical data about effects of the treatment through a process called meta-analyses. Then authors assess the evidence for any benefits or harms from those treatments. In this way, systematic reviews are able to summarise the existing clinical research on a topic.

Five steps in a systematic review:

1. Formulate your question
2. Search for studies
3. Assess the quality of studies
4. Summarise the evidence
5. Interpret the findings

The following books (available as e-books using the links below) provide good introduction for those new to conducting a systematic review, or those looking for a refresher.

Systematic reviews of medical interventions are carried out over a long period of time (mean: 67.3 weeks) and good quality, rigorous systematic reviews require multiple authors and experts to support the different stages of the review process.

Systematic reviews must follow a study protocol which details the methods to be used in the review. Protocols are essential to ensuring a rigorous approach and can help verify that previous systematic reviews have not already answered the research question.

Systematic reviewers should search multiple bibliographic databases to ensure that they have been comprehensive in their approach, and utilise other searching methods such as hand-searching to ensure all trials, or relevant studies are identified. Hand-searching is a manual process whereby an author identifies relevant studies for the review by examining citation lists in journal issues or in grey literature.

There are many other types of review that you can undertake and often these are defined by the amount of time you have and the amount of literature that is available. To learn more about different review methodologies and understand which type of review will best to undertake, we recommend you read ths following article: 

Grant, M.J. and Booth, A. (2009), A typology of reviews: an analysis of 14 review types and associated methodologies. Health Information & Libraries Journal, 26: 91-108. doi:10.1111/j.1471-1842.2009.00848.x

Would you like to see some examples of systematic reviews?

The resources below are useful for locating systematic reviews: 


Quickly identify systematic reviews for decision making. This resource brings together details of systematic reviews indexed in a range of different research databases.

TRIP database

Run your search and then refine by evidence type on the right hand side. The options include systematic reviews.

The Cochrane Library

The Cochrane Library includes evidence from Cochrane and other systematic reviews, protocols and clinical trials.

NICE Evidence search

Run your search, and then from the options on the left hand side, select Types of information and choose from a list that includes systematic reviews and guidelines.


Run your search and then refine by article type. Click on more to see the full list.

Also try PubMed Clinical Queries (select from the home page of PubMed). Run a search for a topic, and the systematic reviews will be displayed in the middle column.

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