Editors: Denise O’Connor, Sally Green and Julian PT Higgins.
Key Points
A clearly defined, focused review begins with a well framed question. In Cochrane reviews, questions are stated broadly as review ‘Objectives’, and specified in detail as ‘Criteria for considering studies for this review’.
The review question should specify the types of population (participants), types of interventions (and comparisons), and the types of outcomes that are of interest. The acronym PICO (Participants, Interventions, Comparisons and Outcomes) helps to serve as a reminder of these. These components of the question, with the additional specification of types of study that will be included, form the basis of the pre-specified eligibility criteria for the review.
Cochrane reviews should include all outcomes that are likely to be meaningful, and not include trivial outcomes. Primary outcomes should be limited to a very small number and include adverse as well as beneficial outcomes.
Cochrane reviews can focus on broad questions, or be more narrowly defined. There are advantages and disadvantages of each.
5.1 Questions and eligibility criteria
5.2 Defining types of participants: which people and populations?
Box 5.2.a: Factors to consider for 'Types of participants'
5.3 Defining types of interventions: which comparisons to make?
Box 5.3.a: Factors to consider for 'Types of interventions'
5.4 Defining types of outcomes: which outcome measures are most important?
Box 5.4.a Factors to consider when developing criteria for 'Types of outcomes'
5.6 Defining the scope of a review question (broad versus narrow)
Table 5.6.a: Some advantages and disadvantages of broad versus