What is PRISMA, and why do you need a protocol?
PRISMA stands for Preferred Reporting Items for Systematic reviews and Meta-Analyses.
If you are planning on publishing your systematic review then you will want to follow the PRISMA guidelines and checklists, as this is the standard format for reporting systematic reviews.
For example, if you have read any systematic reviews you will have seen they include items like the PRISMA flow diagram. It is useful to be familiar with PRISMA before you write your protocol and embark on your review. The following resources may be helpful:
- PRISMA website
- The PRISMA 2020 statement: an updated guideline for reporting systematic reviews, BMJ 2021; 372. https://doi.org/10.1136/bmj.n71.
- PRISMA 2020 Checklist
- PRISMA 2020 Flow Diagram.
You may wish to use a spreadsheet, such as the one provided by the Cochrane Airways Group, to record items you will need to complete your PRISMA flow diagram. We highly recommend documenting all stages of your review to help with reporting.
What is a protocol?
Once you have decided that your systematic review is viable then you need to write a protocol. This is a plan of how you will conduct your review. It will make it easier to understand what needs to be done at each stage of your review.
At this point you may decide to refine your research question further and break it down using one of the common frameworks available. These frameworks can also help you create your search strategy.
For example, the most common framework used in health reviews is PICO:
- Intervention or Issue
- Comparison (if any)
See our guide on Planning a search using PICO [PDF, 185 KB].
There are other frameworks available and you should pick the one most useful to you. In some subject areas there may not be a relevant framework to use.
- PICO variants = PICOT (T is time within which the outcome will be observed, or study type) and PICOS (S is study type).
- PECO = Population, Exposure, Comparison, Outcome.
- PIRT = Population, Index Test, Reference Test, Target Condition.
- SPIDER = Sample, Phenomenon of Interest, Design, Evaluation, Research Type.
- PCC = Population/Problem, Concept, Context (for Scoping Reviews).
Inclusion and Exclusion Criteria
When you are writing your protocol and thinking about your search strategy you will need to define your inclusion and exclusion criteria. This is the criteria you will use to decide if a study is eligible to be included in your review.
Examples of Inclusion/Exclusion Criteria
- Study design – what type of studies are you including in your review? Quantitative, qualitative or both? Are you only going to include specific study types e.g. randomised controlled trials?
- Population – are you looking at a specific population e.g. by age, gender, ethnicity or geography?
- Years of publication – are you limiting your review to a certain range of years e.g. the last ten years? It is advisable to have a robust reason for limiting by year. You might be updating an older review; a guideline or treatment came into effect from that date etc.
- English language only – many reviews do limit to English language only publications for practical reasons, but if you do this you must acknowledge it is a weakness in your review.
- Webinar from the Centre for Open Science on developing inclusion/exclusion criteria: Screening for studies in systematic reviews, scoping reviews, and other knowledge syntheses: Strategies for improvement (April 2020).
- Chapter 3 of the Cochrane Handbook: Defining the criteria for including studies and how they will be grouped for the synthesis.
- PRISMA for systematic review protocols (PRISMA-P).