Seventy percent of studies supported the idea that patients undergoing a procedure are less likely to die if their hospital or physician does large numbers of such procedures. This finding was strongest for AIDS treatment and for surgery on pancreatic cancer, esophageal cancer, abdominal aortic aneurysms, and pediatric heart problems. For these procedures, the authors estimated that using “low-volume” hospitals or physicians resulted in approximately 3 to 13 additional deaths per 100 patients. They found limited evidence and weaker volume–outcome relationships for heart surgery, surgery for other types of cancer, and orthopedic procedures. Most studies took into account patient characteristics such as age, but only 28% made statistical corrections that allowed them to compare low-volume and high-volume care in patients with similar general health, a factor that could affect the results of surgery.