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Systematic Reviews: Before you begin

A guide for researchers undertaking a systematic review

Before you begin


Systematic reviews aim to answer a single research question.

There are many mnemonics available to assist you to formulate a search strategy based on the type of review you are undertaking and the kind of question you are asking.

Mnenomic Explanation Used for...
PICO(S) Population - Intervention - Comparator - Outcome - (Study design) Reviews of effectiveness
PICo Population - Phenomena of Interest - Context Qualitative reviews
Expert opinion / Policy
PEO Population - Exposure - Outcome Aetiology and Risk
CoCoPop Condition - Context - Popuation Prevalence and Incidence
PIRD Population - Index test - Reference test - Diagnosis of interest Diagnostic test accuracy
PCC Population - Concept - Context Scoping reviews
PICOC Population - Intervention - Comparator(s) - Outcome - Context Costs / Economic evaluation
CPIMP Construct of interest - Population - Type of measurement instrument - Measurement properties Psychometric
PFO Population - Prognostic Factors - Outcome Prognostic


Use the above mnemonics to construct your research question and break down your search strategy. Remember that equal emphasis may not be put on each part of the mnemonic, and will largely depend on the topic of your systematic review.

Population How would I describe a patient/problem/situation similar to mine? 
Intervention Which main intervention am I considering? 
Comparison What is the main alternative?
Outcome What could this intervention accomplish, measure, improve or affect?
Study design Which study design will best answer my question?


It is important to be aware of whether other systematic reviews answering your research question or similar research questions, have already been conducted or are in process. This will help avoid duplication of effort and resources as well as be a guide in terms of the construction of your search strategy. 

To locate existing systematic reviews you can try: 

It is highly recommended that you register or publish your systematic review protocol prior to undertaking the review. This:

  • limits duplication of reviews by allowing identification of topics already under review;
  • allows peer-review of protocol, and;
  • provides a base of evidence to critically analyse the review versus protocol once complete.

For systematic reviews related to health sciences, PROSPERO is a highly respected international review register. Some journals also provide scope to publish systematic review protocols in other subject areas.