. "How is Volume Related to Quality in Health Care?." Interpreting the Volume-Outcome Relationship in the Context of Health Care Quality: Workshop Summary. Washington, DC: The National Academies Press, 2000.
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Interpreting the Volume–Outcome Relationship in the Context of Health Care Quality: Workshop Summary
Dr. Hillner presented data to show that any policies directing patients to high-volume centers would affect many people, because lower-volume facilities account for a significant fraction of patient care. In Maryland from 1992 to 1996, for example, 36 percent of surgeries for colon cancer were performed by surgeons treating fewer than 5 cases per year (average, 2 per year). Three-quarters of the surgeons performed 10 or fewer surgeries per year. By contrast, in Ireland where care is concentrated in high-volume settings, 80 percent of surgeons who do colectomies perform 10 or more surgeries for colon cancer per year. Dr. Hillner suggested that most individuals, when informed of the relationship between volume and outcome, would not find current practices in the United States acceptable.
Dr. Hillner suggested some parallels between programs to promote selective referral for surgical procedures and disease management programs for patients with chronic conditions. For both, patient care resources are concentrated. Establishing the relationship between volume and outcomes for hospital-based procedures has been somewhat easier because of the availability of large databases containing information on hospital outcomes. There is somewhat less evidence of the success of disease management because of the limitations of available data and the need to examine longer-term outcomes of chronic diseases such as diabetes.
Dr. Milstein observed that causal models to explain favorable hospital outcomes are in a primitive state. He supported the notion that process measures of quality would be preferable to volume and the consequent need for a significant expansion of routinely collected data elements. Dr. Milstein noted, however, major resistance to such expansion on both national and state levels (especially data to assess the performance of individual physicians). Dr. Milstein questioned the assumption that the most valuable use of volume–outcome research will be for quality improvement. This assumption reflects a faith that the health industry's weak quality improvement capabilities will improve and that little of the association of volume with outcome will ultimately be rooted in volume-influenced proficiency. It may be the case that the frequency of real-world exercise of physical and mental skills will remain important, even after low-volume hospitals are made aware of the “tricks” of the high-volume trade. Since hospital performance differences are likely to persist after provider-to-provider knowledge transfer, Dr. Milstein recommended that social science research be expanded to improve understanding of consumers' use of quality indices in choosing hospitals and physicians. He noted that the existing literature suggests that the use of provider quality comparisons by consumers is not likely to result from today's “information dump of statistical tables.” This will require simplification of information, putting it into multiple formats, and having it conveyed by trusted sources. Lastly, although Dr. Milstein agreed with the need for caution in using volume-based indicators, he questioned whether any workshop participants would commit to personally receiving complex treatments at the nearest low-volume hospital in their health plan's network. He suggested that this is what we currently tolerate for less well educated Americans who live near low-volume hospitals.
Discussion moderator Dr. Sisk asked workshop participants to consider the types of measures needed to implement policy and to assess the adequacy of risk-adjustment methodologies. Two main applications of studies of the volume outcome relationship were identified in the discussion. The first is research, identifying whether a relationship exists and the factors that affect the relationship. For these purposes, available risk-adjustment methods are adequate, even when applied to administrative data. According to Dr. Halm, the literature review suggested that risk adjustment, although important, did not greatly affect the magnitude of the association between volume and outcome. The second application is to provide information to individual providers of care as part of a quality improvement program or to inform consumers of the volume or out-