Group Health Cooperative Of Puget Sound

Group Health Cooperative of Puget Sound (GHC) is a health maintenance organization (HMO), established in 1947, which provides health care on a prepaid basis to approximately 415 000 persons in western Washington State, located in the northwestern corner of the United States (Saunders et al., 2000). Most of these enrollees receive all their care at Group Health facilities. An additional 47 000 residents of western Washington belong to a subsidiary of GHC, established in 1990, which provides a "point of service'' option that permits care from community providers other than Group Health providers. As the point of service coverage is more expensive than that provided by Group Health providers, most of the coverage remains within the Group Health network. Although the majority of enrollees receive health benefits through their place of employment, coverage has been extended to 54 000 Medicare, 25 000 Medicaid, and 26 000 Washington Basic Health Plan recipients, thereby expanding its membership to include elderly and low-income residents (Saunders et al., 2000).

GHC offers comprehensive health care coverage for outpatient care, inpatient services, emergency care, mental health services, and prescribed drugs, although the latter are not provided to Medicare enrollees new to GHC since 1994. Nearly all benefit plans require small co-payments for services, such as prescriptions, outpatient visits unrelated to preventive care, and emergency treatment. Coverage for outpatient drugs is controlled by GHC's drug formulary.

At GHC, each enrollee is assigned a unique number, which remains with that person even if the individual drops out of the plan and then rejoins the health system at a later date. Multiple databases have been developed from the main database, with an individual's records linked through their unique number.

The socio-demographic profile of GHC enrol-lees is generally comparable to that of the population of the Seattle-Tacoma area, with the GHC enrollees somewhat better educated. The median income of both groups is similar, although the GHC membership is less representative of the highest income category.

Multiple database files exist, and date from varying time-points. The current enrollment file consists of some 460 000 individuals; historical files contain records for some 2 million persons ever enrolled in GHC; 1.5 million persons have been enrolled since 1980 (Saunders et al., 2000). The Pharmacy file, dating from 1977, includes records generated when prescriptions are filled. The drug data include drug number, therapeutic class, drug form and strength, date dispensed, quantity dispensed, cost to GHC, and refill indicator. The file currently includes a field for number of days the medication should last. The hospital database, dating back to the early 1970s, includes diagnoses, procedures, diagnostic-related group (DRG) and discharge disposition. Laboratory data are available since 1986, and specify the test ordered, the date ordered, specimen source, results, and date of the results. All radiographic studies performed at GHC facilities, including MRI and CT scans, are now available in the outpatient visits file. Beginning in the early 1990s, diagnosis and procedure data were incorporated into the outpatient registration database, which also includes date of visit, the provider seen, the provider's specialty, and the location of care.

As a longtime participant in the National Cancer Institute's SEER program (Cancer Surveillance, Epidemiology, and End Results), GHC receives a data file of all newly diagnosed cancers among its enrollees, including anatomical site, stage of diagnosis, and vital status at follow-up. The Fred Hutchinson Cancer Research Center in Seattle maintains a Cancer Surveillance System, consisting of the 13 contiguous counties of northwest Washington, and is one of the 13 SEER population-based registries in the United States (see http:// seer .cancer. gov/AboutSEER.html).

GHC has also developed a death file that covers enrollees between the years 1977 and 1997. Data are also available from the Community Health Services department, an immunizations database, and from claims databases for services purchased from non-GHC providers. Cost information is available through the Utilization Management/Cost Management Information System, developed in 1989.

Turnover in membership at GHC is estimated to be approximately 15% per year (Saunders et al., 2000). Since Group Health has been in existence for more than 50 years, a subset of enrollees can be identified whose tenure spans decades.

Limitations to the GHC databases include its small size, a disadvantage in the study of uncommon outcomes as most drugs are used by only a small percentage of the population; the lack of information on some important confounders, such as smoking and alcohol consumption; loss of drug coverage for its Medicare enrollees; and limitations of the GHC formulary, especially with regard to newly marketed drugs, since GHC may decide not to add a new drug or may delay its adoption until it has been on the market for a while. Drugs that offer little therapeutic or cost advantage over drugs already listed on the formulary may be excluded. Non-formulary drugs, such as sildenafil, fenfluramine, and phentermine, may be purchased for use outside the GHC pharmacy system, and therefore would not be represented in the database.

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