Three Step Process for Defining Hospital Service Areas

Hospital service areas were defined through a three-step process. First, all acute care hospitals in the 50 states and the District of Columbia were identified from the American Hospital Association and Medicare provider files and assigned to the town or city in which they were located. The name of the town or city was used as the name of the hospital service area, even though the area might have extended well beyond the political boundary of the town. For example, the Mt. Ascutney Hospital is in Windsor, Vermont. The area is called the Windsor hospital service area, even though the area serves several other communities.
 

In the second step, all 1992 and 1993 Medicare hospitalization records for each hospital were analyzed to ascertain the ZIP Code of each of its patients. When a town or city had more than one hospital, the counts were added together. Using a plurality rule, each ZIP Code was assigned on a provisional basis to the town containing the hospitals most often used by local residents.

The analysis of the patterns of use of care by Medicare patients led to the provisional assignment of five post office ZIP Codes to the Windsor hospital service area

ZIP Code	Community Name	1990 Population	% of Medicare Discharges to Mt. Ascutney Hospital
05037	Brownsville	415	52.8
05048	Hartland	1,730	46.8
05053	Pomfret	245	52.6
05062	Reading	614	36.8
05089	Windsor	5,406	63.2

The third step involved the visual examination of the ZIP Codes using a computer generated map to make sure that the ZIP Codes included in the hospital service areas were contiguous. In the case of the Windsor area, inspection of the map led to the reassignment of Pomfret to the Lebanon hospital service area. In the final determination, the Windsor hospital service area contained four communities and a total population of 8,165.

Map 1.1. ZIP Codes Assigned to the Windsor, Vermont, Hospital Service Area

The analysis of the pattern of use of hospitals revealed that Medicare enrollees living in the five ZIP Code areas in light blue most often used the Mt. Ascutney Hospital in Windsor, Vermont. To maintain geographic continuity of hospital service areas, the Pomfret ZIP Code 05053 was reassigned to the Lebanon hospital service area. The Windsor hospital service area contained four communities, with a 1990 census of 8,165. During 1992-93, there were 679 hospitalizations among the Medicare population; 394 (58%) were to Mt. Ascutney Hospital, 131 to the Mary Hitchcock Memorial Hospital, and 154 to other hospitals.