Description is the start of any epidemiologic analysis, and quickly leads to questions of causation. What factors lead to high medical practice variation? Can we say that some types of medical practice variation are “good” and other types “bad?” If we determine the causes, are there remedies that might improve health care and health? At this early stage, there are no specific answers to these questions for Israel. Inferential analysis of the causes and health consequences of variation proceeds much more slowly than description. But there is a sizable body of inferential research from other countries that may have relevance to Israel [
5].
The primary motivation to study patterns of health care utilization is to gain insight into the performance of health care providers and systems. Suboptimal health care performance has consequences for population health, but variation in health care is only partially explained by area population differences. The technical term for the variation that is not explained by patient needs or preferences is “unwarranted variation” and reflects differences in health care quality and efficiency. Originally, analyses examining unwarranted variation were termed “small area analysis,” [
6] in reference to analysis across empirically defined health care service
areas (i.e. geographic health care markets). With improvements in data quality, recent efforts have been directed toward the measurement across
providers, such as hospitals. Regardless of the units that define the population or patient denominators, the study of health care variation faces similar challenges in methods and interpretation.
While the first study of medical practice variation was published in England in 1938, [
7] John Wennberg’s 1973 paper in
Science reporting differences in health care resources and utilization across the relatively homogenous State of Vermont marked the beginning of rapid growth in small area analysis studies in the U.S. [
8]. Given today’s recognition of the uneven shortcomings in health care, it may be difficult to appreciate that in the 1970s these findings were initially ignored, later attacked, [
9] before being replicated [
10‐
12] and then widely embraced by clinicians, health system administrators and policy makers in the U.S. Canada, and the U.K. A notable testament to the seminal character of Wennberg’s paper is its citation by over 1200 other academic papers [
13]. Subsequent studies by Dr. Wennberg and his Dartmouth colleagues further advanced the methods to interpret regional patterns of care from the beginning to the end of life [
14,
15]. Cohort studies were developed to address inherent weaknesses in cross-sectional designs, and ecologic analyses were supplanted by multi-level models with the patient as the unit of analysis [
16‐
18]. With funding from the Robert Wood Johnson Foundation in 1992, Wennberg and colleagues introduced the
Dartmouth Atlas of Health Care series (see
www.dartmouthatlas.org) as a dissemination tool directed towards non-academic audiences, such as health care administrators, health policy makers, and congressional staffers. At the same time, research into health care variation grew in the U.K. and Canada, and more recently, with strong support from national and provincial health ministries [
5]. In the past 40 years, these and other studies of unwarranted variation have influenced the practice of medicine, the organization of delivery systems, the financing of medical care, and national health care policy.