Attributing practice variation by its sources: the case of varicose veins treatments in the Netherlands.

Background: Unwarranted practice variation refers to regional differences in treatments that are not driven by patients' medical needs or preferences. Although it is the subject of numerous studies, most research focuses on variation at the end stage of treatment, i.e. the stage of the treating specialist, disregarding variation stemming from other sources (e.g. patient preferences, general practitioner referral patterns). In the present paper, we introduce a method that allows us to measure regional variation at different stages of the patient journey leading up to treatment.

Methods: A series of logit regressions estimating the probability of (1) initial visit with the physician and (2) treatment correcting for patient needs and patient preferences. Calculating the coefficient of variation (CVU) at each stage of the patient journey.

Results: Our findings show large regional variations in the probability of receiving an initial visit, The CVU, or the measure of dispersion, in the regional probability of an initial visit with a specialist was significantly larger (0.87-0.96) than at the point of treatment both conditional (0.14-0.25) and unconditional on an initial visit (0.65-0.74), suggesting that practice variation was present before the patient reached the specialist.

Conclusions: We present a new approach to attribute practice variation to different stages in the patient journey. We demonstrate our method using the clinically-relevant segment of varicose veins treatments. Our findings demonstrate that irrespective of the gatekeeping role of general practitioners (GPs), a large share of practice variation in the treatment of varicose veins is attributable to regional variation in primary care referrals. Contrary to expectation, specialists' decisions meaningfully diminish rather than increase the amount of regional variation.