This study looks at a variety of factors that may affect Health Mainte
nance Organization (HMO) efficiency, focusing on the economic incentiv
es that derive from ownership. Previous studies have found that HMO ef
ficiency depends largely on the extent to which ambulatory services su
bstitute for inpatient services. Our analysis supports this conclusion
, but takes it one step further. We demonstrate that owners who also p
rovide health care services-specifically physicians and hospitals-may
have an incentive to use more of their particular service. Our empiric
al results show that hospital-owned HMOs do in fact use more inpatient
services than do HMOs owned by physicians or others, indicating that
hospital-owned HMOs will be less efficient.