Abstract
The randomized ISAT demonstrated the superiority of endovascular treatment in patients with ruptured intracranial aneurysms considered suitable for either clipping or coiling. A later publication proposed a second look at the results, demonstrating that older patients with ruptured MCA aneurysms appeared to benefit from clipping, in disagreement with the general findings of the trial. Subgroup analyses in randomized trials and observational studies examine whether effects of interventions differ between subgroups according to the characteristics of patients. However, many apparent subgroup effects have been shown to be spurious. Misleading subgroup effects can result in withholding efficacious treatment from patients who would benefit or can encourage ineffective or potentially harmful treatments for patients who would fare better without. Some guidelines for the prudent interpretation of subgroup findings are reviewed.
Highlights
In the example we have chosen, Ryttlefors et al[3] emphasized the superiority of clipping over coiling for MCA aneurysms (OR, 7.8; 95% CI, 1.4 – 43.1; P ϭ .02) and the superiority of coiling over clipping for internal carotid arteryϪposterior communicating artery aneurysms (OR, 0.4; 95% CI, 0.2–1.0; P ϭ .04) in patients older than 65 years, in effect comparisons of subgroups based on location within subgroups based on a dichotomy according to age, an analysis that raises numerous concerns
What Can Give Support to a Subgroup Finding? many subgroup findings should not be trusted, there are clues that enable readers to give some credence to subgroup effects
To use trial results with confidence in the treatment of future patients, we need reassurance that the same treatment benefited a diversity of patients, with varying prognostic factors of clinical interest that might have an impact on the treatment effect
Summary
The Problem of Subgroup Analyses: An Example from a Trial on Ruptured Intracranial Aneurysms. Subgroup Analysis in Randomized Controlled Trials and Observational Studies Treatment recommendations obtained from the overall results of RCTs do not necessarily apply to any particular individual When both coil embolization and clip ligation are considered appropriate options, ISAT has shown that coil embolization, in general, leads to a better outcome at 1 year. All physicians, confronted with a treatment decision in a particular patient, would like to know the evidence that pertains most directly and most to that individual In both RCTs and observational studies, investigators, trying to meet clinicians’ expectations for specific information, frequently conduct subgroup analyses that explore multiple hypotheses. In the example we have chosen, Ryttlefors et al[3] emphasized the superiority of clipping over coiling for MCA aneurysms (OR, 7.8; 95% CI, 1.4 – 43.1; P ϭ .02) and the superiority of coiling over clipping for internal carotid arteryϪposterior communicating artery aneurysms (OR, 0.4; 95% CI, 0.2–1.0; P ϭ .04) in patients older than 65 years, in effect comparisons of subgroups based on location within subgroups based on a dichotomy according to age, an analysis that raises numerous concerns
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