The study took place in Group Health Cooperative
(GHC), a mixed-model HMO providing health
services to approximately 400,000 adults in western
Washington state. Founded in 1947, GHC is the
nation’s oldest and largest consumer-governed
HMO. GHC contracts with the Group Health Permanente
medical group to provide care for the 85%
of the plan’s enrollees receiving care within a groupmodel
delivery system, whereas the remainder are
cared for in a network-model system. GHC’s enrollees
are not representative of the entire nation but
are representative of the communities in which it
provides care [13]. Group Health offers a comprehensive,
coordinated care Medicare + Choice plan
and was the first health plan in the United States to
provide Medicare services on a prepaid, capitated
basis. Approximately 75% of seniors in GHC have
a prescription drug benefit as part of their medical
coverage. GHC discontinued an outpatient drug
benefit for new individual Medicare enrollees instatus