Geographic variations in medical care have been studied extensively since at least the early 1970s. Consistent findings over decades of research are that variations are ubiquitous and that much of the variation is unwarranted because it is not explained by variations in illness or patient preferences [[1], [2], [3]]. Unwarranted variations have remained relevant in health policy because of the implied potential to substantially improve outcomes and reduce costs by redressing them. Variations studies often classify health services into the categories first proposed by the Dartmouth Atlas Project [4]: effective care, preference sensitive care, and supply sensitive care. This classification is useful because the optimal policy interventions to reduce variations will vary by service category [1,5]. For example, supply sensitive services are those whose use can be discretionary and is strongly correlated with resource supply.

Echocardiography is the most common cardiac diagnostic exam, providing information essential to the evaluation of approximately one hundred cardiac presentations and conditions [[6], [7], [8]]. Like most diagnostic services, echocardiography is a supply sensitive service. There are no definitive clinical-science based standards governing its use in all circumstances. In Canadian and international jurisdictions, echocardiographic services have been characterized by marked regional variations [[9], [10], [11], [12], [13], [14]]. Echocardiography rates have also been shown to be sensitive to the implementation of provider education initiatives, appropriate use criteria, and accreditation processes [[15], [16], [17]].

In this study, we measure geographic variations in echocardiography rates in Ontario and examine the extent to which the variations are explained by differences in population age, sex, cardiac disease prevalence (CDP), and social determinants of health (SDH) risk. We also measure how CDP and access to echocardiography and other cardiac diagnostic services is correlated with SDH risk. By quantifying variations that are uncorrelated with population characteristics, the study aims to determine whether there are important opportunities to improve the echocardiography service delivery system in Ontario. The study also aims to identify methodological and policy implications relevant to the management of supply sensitive services in international settings.