Subgroup analysis is a statistical technique used in research to examine the effects of a treatment or intervention on different subsets of a population. It involves dividing the overall study sample into smaller groups (subgroups) based on specific characteristics or factors, such as age, gender, disease severity, or other baseline characteristics. By doing this, researchers can assess whether the treatment or intervention has different effects in these subgroups.
In systematic reviews, all subgroups should be defined in the protocol: subgroups defined once data has been extracted and/or when analysis starts should be clearly marked as being defined during the systematic review process.