Subgroup analysis can be valuable but requires rigorous standards to avoid pitfalls that can generate spurious or misleading results. It may take discipline to walk away from the seduction of an improper subgroup analysis, especially if there are economic incentives involved.
Requirements for a proper subgroup analysis:
(1) included in the original study design
(2) adequately powered
(3) subjected to appropriate statistical analysis, including formal tests of interaction
(4) clearly described and reported
Any other subgroup analysis is potentially biased. Such an analysis can suggest future studies but should not be accepted as evidence on its own due to inherent weaknesses.
Actions that can contribute to misleading results of an improper subgroup analysis:
