A systematic review is a comprehensive literature search and synthesis project that tries to answer a well-defined question using existing primary research as evidence. A protocol is used to plan the systematic review methods prior to the project, including what is and is not included in the search.

Systematic reviews are often used as the foundation for a meta analysis (a statistical process that combines the findings from individual studies) and to re-evaluate clinical guidelines.

Systematic review and meta analysis are both types of evidence synthesis methods. Read more about evidence synthesis on the Types of Reviews page of this guide.

Consider the following questions before you begin a systematic review: 

1. Is your question suited to a systematic review?

While a systematic review is considered the highest form of evidence, not all questions are suited to a systematic review. A question that is well suited to this methodology is:

• based on a specific question or patient problem and will ensure that your search produces relevant results.
• narrow enough that identifying and reviewing all of the relevant literature is possible. An extremely broad question (e.g. examining pain management and assessment) may be more suited to a general literature review or scoping review.
• broad enough that you will be able to find some relevant literature.  An extremely narrow topic (e.g. an examination of a very small subset of a population) or one that is examining a very new treatment or concept may not return enough relevant literature for a systematic review to be able to draw any meaningful conclusions.
• defined with some consistency across the literature. A question with a multi-stepped intervention, or one in which different elements of an intervention may or may not be included in each study may be more suited to a different approach.

2. Are you asking a clearly defined question?

Thinking about your PICO (population, intervention(s), comparator(s), and outcomes) will help to ensure that you have thought of the important parts of your question, are not omitting any key concepts from your strategy, and assist you in developing your inclusion/exclusion criteria. You can use our PICO worksheet to help develop and refine your question and keywords for your search. 

3. Has a recent systematic review already addressed this exact question?

Before starting your systematic review, you should check for recently published or upcoming reviews on your topic to avoid duplication of effort. Please contact the Ebling Library Systematic Review team if you need assistance searching for existing systematic reviews and registered protocols. 

4. Do you have the time and resources needed to conduct a systematic review?

The mean estimated time to complete and publish a systematic review is 1.3 years, according to a 2017 study. Input from at least 3 team members is needed, in addition to advice or input from a librarian or team member who is experienced in searching the literature. Team members should include someone to oversee the review process, a subject specialist to help decrease the potential for bias to enter your research, and a third team member to break a tie in case of disagreement. 

5. Is a registered protocol required by the journal you are considering for publication of your review?

Many high quality journals require authors to register their protocols with PROSPERO or other protocol registry sites. PROSPERO will not accept protocols after data extraction has begun, so following the author guidelines for the journal you have identified for publication is an important part of getting published. If you need help identifying potential journals for publication, see our Where Should I Publish Guide or contact an Ebling Librarian for assistance. 

6. Can you meet all of the requirements for a systematic review detailed in the PRISMA checklist?

The PRISMA group created a checklist of items for systematic review protocols that should be followed to ensure thoroughness and transparency in reporting. You should consider registering your protocol with PROSPERO to allow for peer review and to avoid duplication of effort. 

Parts of this guide are adapted from "Systematic Reviews" by Taubman Health Sciences Library, University of Michigan, used under CC BY 4.0.