Subgroup analysis refers to repeating the analysis of a study within subgroups of subjects defined by a subgrouping variable (e.g. smoking status defining two subgroups: smokers and non-smokers).
Aim
The aim of subgroup analysis is usually to assess whether the association of two variables differs depending on a third variable. For instance, investigators of a study testing the effect of an intervention (variable 1) on preventing
heart attack
A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which ma ...
s (variable 2) might be interested in whether the effect varies by smoking status (variable 3). Therefore, they could perform separate analyses for smokers and non-smokers, and then compare the results. If results differ, there is a subgroup effect.
Terminology
The terminology is inconsistent. Alternative names for subgrouping variables include effect modifiers, predictive factors, or moderators. Alternative names for subgroup effects include effect modification and interaction. Some authors define effect modification and interaction differently, and distinguish different types of interaction. A more unspecific term is heterogeneity of treatment effects.
See also
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Post-hoc analysis
In a scientific study, post hoc analysis (from Latin '' post hoc'', "after this") consists of statistical analyses that were specified after the data were seen. They are usually used to uncover specific differences between three or more group mea ...
References
Statistical analysis
Design of experiments
Medical statistics
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