A systematic review attempts to identify, appraise and synthesize all available relevant evidence that to answer a specific, focus research question. Researchers conducting systematic reviews use standardized, systematic methods and pre-selected eligibility criteria to reduce the risk of bias in identifying, selecting and analyzing relevant studies.
Prepared by the Cochrane Consumers and Communication Group, La Trobe University and generously support by Cochrane Australia. Written by Jack Nunn and Sophie Hill.
Traditional literature reviews differ from systematic reviews in many ways, and especially on how they are conducted and time commitment required.
When systematic reviews SHOULD be done:
If you have a clearly defined research question with established inclusion and exclusion criteria
To test a specific hypothesis to ensure a manageable results set
When there is a large body of primary research on your specific research question
When you have team of at least three people assembled to help conduct the systematic review
When a transparent search methodology and replicability are needed
When an existing systematic review is outdated (consider updating the existing review)
When no ongoing or existing systematic review addresses your research question
When Systematic reviews SHOULD NOT be done:
If you do not have a clearly defined research question.
Systematic reviews without a clear and specified research question with details such as populations, interventions, exposures, and outcomes, will produce large and inconsistent search results to screen, and offer no consistent way to assess and synthesize findings from the studies that are identified.
If you do not have enough time to complete the review systematically
Systematic reviews are a lot of work. Including creating the protocol, building and running a quality search, collecting all the papers, evaluating the studies that meet the inclusion criteria and extracting and analyzing the summary data, a well done review can require dozens to hundreds of hours of work that can span several months.
If you plan to do a systematic review on your own
All systematic review guidelines recommend that at least two subject experts screen the studies identified in the search. The first round of screening can consume 1 hour per screener for every 100-200 records. A systematic review is a team effort.
Systematic reviews require time and effort to complete. It should not be expected to complete a systematic review in a matter of months. The average time to complete a systematic review is between 12-18 months. Different types of evidence synthesis, such as Rapid Reviews, can be completed in a shorter amount of time.
The PredicTER tool helps provide an estimate of a systematic review timeline.
A systematic review can't be done alone. You should carefully consider all of the expertise you will need to define your research question, search for evidence, appraise/grade the evidence, and potentially complete a statistical meta-analysis of the data. A recommended systematic review team would consist of the following: