• cancer surgery,

• percutaneous transluminal coronary angioplasty (PTCA),

• acute myocardial infarction, and

• acquired immunodeficiency syndrome (AIDS).

Their review focused on the nature of the relationship between volume and outcome, the causal pathways that might explain the relationship, and whether the research findings might apply to other clinical areas. Historically, the volume–outcome relationship has been explained by “practice makes perfect” or patient selection (i.e., “busy doctors see healthier patients”). The authors propose a conceptual model that identifies a series of factors that might underlie the relationship between volume and quality of care (Figure 1).

The authors conclude that for a wide variety of surgical procedures and medical conditions, higher volume (whether assessed by hospital or by physician) is associated with better health outcomes. The uniformity with which the published research documents or confirms the existence of this association is compelling (although the review authors caution that a publication bias against negative findings cannot be ruled out):

• Statistically significant associations between higher volume and better outcomes were found in 79 percent of the studies of hospital volume and 77 percent of the studies of physician volume.

• None of the studies reviewed showed a negative effect of volume.

• A significant volume effect was observed in all 16 of the studies judged to have the soundest research methods.

A higher-volume, better-outcome association was observed in three-quarters of the studies

reviewed. There is, however, great variation in outcomes, especially for low-volume providers. Some low-volume providers have excellent outcomes, and conversely, some high-volume providers have very poor outcomes. Furthermore, the performance gap between low- and highvolume hospitals appears to narrow with time as procedures become well established (e.g., the

Front Matter (R1-R6)

Contents (R7-R8)

Abstract (1-1)

Introduction (1-2)

Why Does the Volume-Outcome Relationship Matter? Who Cares and How Could it Be Used? (3-3)

How is Volume Related to Quality in Health Care? (4-9)

What Are the Policy Implications of a Volume-Outcome Relationship? (10-16)

Where Do We Go From Here? (17-18)

Appendix A: Workshop Agenda and Participants (19-22)

Appendix B: Members of the Committee on Quality of Health Care in America and the National Cancer Policy Board (23-26)

Appendix C: How is Volume Related to Quality in Health Care? A Systematic Review of the Research Literature? (27-102)

Appendix D: When and How Should Purchasers Seek to Selectively Refer Patients to High-Quality Hospitals? (103-119)