In 1986, Wennberg (1), the influential founder of the Dartmouth Atlas project on geographic differences in health care, wrote a piece entitled "Which rate is right?," in which he described the great variability in health care delivery that existed at the time. He posited that such variability resulted not just from correct and incorrect medical decisions but also from legitimate differences in opinion about tests' and treatments' safety and efficacy. We have made great strides in attempting to standardize what it means to be safe or efficacious, but the distinction between appropriate and inappropriate care remains elusive.In trying to understand these practice differences and the potential errors of omission or commission that they contain, organized information is an essential ingredient. There is perhaps no greater success story in this regard than the country's largest integrated health system-the Veterans Affairs (VA) Health System. Responding to accusations of suboptimal care in the 1980s and 1990s, the VA restructured its health care system into 22 geographically organized networks (2). Standardized quality metrics were applied across networks, often characterized by the proportion of a given network receiving evidence-based services. The VA subsequently showed significant improvement in many measurable aspects of care delivery. For example, the rate of pneumococcal vaccination increased from 29% in 1995 to 90% by 2003.However, even with transparency, uptake of recommended care is far from universal. In 2002, Krein et al. (3) measured several quality indicators across 13 VA facilities and found that the proportion of qualifying individuals for whom a lipid profile was measured ranged anywhere from 41% to 84% across facilities. More recently, Pokharel et al. (4) examined the use of statins among over 900,000 veterans with diabetes and found that the rate of statin prescription ranged anywhere from 60% to 83% across 130 VA facilities. These findings draw attention to the large number of veterans not receiving evidencebased care and highlight the variability in care of even common chronic medical conditions. Implicit in these observations is the belief that higher adherence to guideline-based quality measures is better. However, certain aspects of care delivery may not be appropriate for all eligible individuals irrespective of evidence-based practice. For instance, older adults with multimorbidity may have multiple competing guidelines calling for disease-centered quality measures, but they would benefit from a patient-centered approach that intentionally withholds certain tests or treatments (5). It must follow then that some variability in health care delivery is expected, but the challenge is in distinguishing between "appropriate" and "inappropriate" variability.In this issue of the Clinical Journal of the American Society of Nephrology, Navaneethan et al. (6) provide an updated assessment of practice pattern variation that exists in the VA population after implementing quality measures and extend this...