What is a systematic review?
A systematic review is a literature overview that attempts to answer a well-defined question in a rigorous way. The term ‘systematic’ indicates that special care was paid to the methods used for searching, selecting, analyzing, and reporting of the data. A critical appraisal of the included studies is also an important part of a systematic review. Rigorous systematic reviews are transparent with regard to its methods, thus allowing the reader to form an opinion on both the quality of the evidence presented and the quality of the review itself. This rigorous method minimizes the risk of bias and therefore results in the ‘best available evidence’ concerning a specific topic.
The overall aim of a systematic review is providing reliable evidence to anyone involved in healthcare decision-making; healthcare professionals, caretakers, patients, policy makers, making sure they are able to make informed decisions, resulting in better health outcomes.
Cochrane is a nonprofit organization that provides guidance and support to researchers and healthcare professionals who want to write high-quality systematic reviews. Importantly, Cochrane reviews always concern a clinical intervention or diagnostic test, thus being of direct relevance to clinical practice.
Furthermore, Cochrane tries to disseminate the evidence collected in its reviews as widely as possible. Every Cochrane review must contain a ‘plain language summary’. Additionally, Cochrane actively promotes translation of its reviews and summaries in local languages, thus decreasing the barrier towards Cochrane evidence for non-native English speakers.
Due to the rigorous methodological requirements, Cochrane reviews are considered the gold standard in systematic reviews, and Cochrane evidence is easily picked up by popular media, policy makers and healthcare practitioners.
Finally, Cochrane reviews are, in contrast to other (systematic) reviews, regularly updated. Therefore, they are a convenient way to keep updated about the best available knowledge for a certain intervention.
How to start a Cochrane systematic review
Belgian researchers or healthcare professionals who would like to write a (Cochrane) systematic review can be supported by Cochrane Belgium. Below you can find the different steps in this process.
Step 1: Before you start
Before starting, we recommend to register to our Systematic Review courses Part I and II. Furthermore, we suggest to take a look at the Cochrane Handbook. This takes some time, but will pay off later in the review process.
Upon selecting a topic to write a Cochrane review about, it is a good idea to check the Cochrane Library to see if no one else is already working on this topic. This to avoid a waste of time and effort. If this is not the case, you can go on and register your title. For this, you have to contact the appropriate review group. We suggest to contact Cochrane Belgium already in this stage of the review process, as we can provide guidance early on and get you in contact with the appropriate review group.
Step 2: Title registration
The title of your review must be registered in the Cochrane Library before starting your review. This title needs to clearly describe the research question at study. Often, the title contains the target population or condition, the interventions that are compared and the outcome of interest. Title registration is done in consultation with the relevant review group. A list of review groups and the procedures to be followed to contact them can be found on the Cochrane website.
It is also required to compose your review team during this stage of the process. Each step in the process of Cochrane reviews must be performed by at least 2 people independently, to prevent errors as much as possible. Take into account that the review team needs to have expertise in the area of review, but also (access to) methodological expertise, including statistical expertise. Often a review group also requires involvement of an author with previous experience in writing a Cochrane review. Please contact Cochrane Belgium if you encounter problems with the composition of your review team.
The review group’s coordinator will make a judgment about your review proposal, based on availability of the topic, appropriateness regarding the scope of the review group and priority of the topic. If the topic is already under review by another group, you will look for a compromise, where often the two candidate review groups join forces. If the topic is available, the title is likely to be accepted and you can start writing the protocol. If the review group considers your topic to be out of scope, another review group can be suggested.
Step 3: Writing the protocol
Writing the protocol is a very important step, which requires reflection and deliberation with the whole review team, because the protocol will be subject to peer review and published in the Cochrane Library in advance. The protocol needs to be followed meticulously during the review process and any deviation to the protocol has to be documented appropriately. It already contains:
- Background information
- Objectives of the review
- In- and exclusion criteria for study selection
- Planned search strategy (databases and search terms to be used)
- Key outcomes at study
- Methods of analysis (data collection methods, statistical model to be used, sub-group analyses planned)
To write the protocol, we recommend to consult the Cochrane handbook. In addition, the freely available RevMan software package (required for writing Cochrane reviews) already contains the structure for the protocol. Finally, it is also recommended to get information from your review group’s coordinator regarding protocol requirements, as each review group has its own rules.
Step 4: Writing your review
After acceptance and publication of the protocol, the review can be conducted according to the protocol. Again, we recommend to look at the Cochrane handbook for detailed instructions. Furthermore, make sure to follow the MECIR (Methodological Expectations of Cochrane Intervention Reviews) standards when performing your review. The previously mentioned RevMan software provides the required structure. After finishing your review, it is again submitted for peer review, before eventual publication.
- Cochrane Belgium is there to provide support if you encounter problems during one of the review steps.
- Authors engaging in writing a Cochrane review are expected to provide periodical updates of their review.