Perspective:

The study suggests that physician adherence to current guidelines regarding referral for CAS and CEA procedures has resulted in clinically and prognostically important differences in the clinical characteristics of patients treated with these procedures. These extreme clinical differences suggest that conducting comparative effectiveness analyses of alternative treatment strategies for carotid revascularization will require large, clinically enriched data sets and sophisticated analytic methods to ensure that valid comparisons are made to guide future clinical practice, and that these comparisons are properly interpreted so that the limitations of these comparisons are transparently conveyed. Even with the use of sophisticated statistical methods, significant residual bias may remain when comparing groups with extreme differences in baseline characteristics.