Technical Report: Methodology for Heart Procedures

Technical Report: Measure development for the Campaign for Effective Patient Care using patient discharge data

Laurence Baker, Ph.D.[1]

The California HealthCare Foundation plans to release findings associated with this measure development effort for the following procedures: angiography, percutaneous coronary intervention (PCI), coronary artery bypass graft surgery (CABG), carotid endarterectomy, hip replacement, knee replacement, cholecystectomy, induction of child birth, cesarean section, vaginal birth after delivery (VBAC), hysterectomy, mastectomy and weight loss surgery. In addition, we developed several other measures using specifications that parallel specifications used in the Dartmouth Atlas that, while not part of the main set of results CHCF will present, are used below in comparisons with results from the Atlas.

1. Overview

The purpose of this analysis is to construct measures of the frequency with which various treatments are used, on a population basis, for HRRs and HSAs in California. The analysis is based on 2005-2009 hospital discharge data from the California Office of Statewide Health Planning and Development (OSHPD). To construct the measures, a set of treatments of interest was defined (see table below), and the number of hospitalizations in which each treatment observed was calculated. Each hospitalization was assigned to the HSA and HRR in which the patient lived. This data was then combined with area population data to produce measures of the rate of use of the treatment, per population. Regression adjustment was used to account for variations across areas in age, sex, race, education, income, and insurance status.

2. HRRs and HSAs

Data in this project are developed for Hospital Referral Regions (HRRs) and Hospital Service Areas (HSAs), according to the definitions developed in the Dartmouth Atlas project. HRRs and HSAs are collections of ZIP codes constructed to define areas appropriate for studying health care utilization.

The Dartmouth Atlas defines HRRs and HSAs as follows:

Hospital Referral Regions (HRRs) represent regional health care markets for tertiary medical care that generally requires the services of a major referral center. The regions were defined by determining where patients were referred for major cardiovascular surgical procedures and for neurosurgery. Each hospital service area (HSA) was examined to determine where most of its residents went for these services. The result was the aggregation of the 3,436 hospital service areas into 306 HRRs [for the entire United States]. Each HRR has at least one city where both major cardiovascular surgical procedures and neurosurgery are performed.

Hospital Service Areas (HSAs) are local health care markets for hospital care. An HSA is a collection of ZIP codes whose residents receive most of their hospitalizations from the hospitals in that area. HSAs were defined by assigning ZIP codes to the hospital area where the greatest proportion of their Medicare residents were hospitalized. Minor adjustments were made to ensure geographic contiguity. This process resulted in 3,436 HSAs [in the entire United States]. When these regions were created in the early 1990s, most hospital service areas contained only one hospital. In the intervening years, hospital closures have left some HSAs with no hospital; these HSAs have been maintained as distinct areas in order to preserve the continuity of the database.

More information about HRRs and HSAs can be found at

This project focused on 24 HRRs designated by the Dartmouth Atlas as falling within California, and 209 HSAs located within those HRRs. There are 13 HSAs that are designated as California HSAs but that are within HRRs that are designated as falling in Nevada, Arizona, or Oregon. These HSAs are excluded.

HRRs are made up of HSAs. Some HRRs cross state boundaries, and include HSAs that fall within more than one state. Based on inspection of the HRR maps in the Dartmouth Atlas,[2] the set of California HRRs appears to contain almost exclusively HSAs that fall entirely within the California state boundaries. The one exception is the Sacramento HRR, which is almost entirely contained in California but appears to contain one HSA that includes part of Nevada.

After the measures were calculated, inspection of data from the South Lake Tahoe HSA suggested the possibility of inaccuracy, likely induced by people from South Lake Tahoe going to hospitals in Nevada for care, which would not be reflected in our data. A choice was made to exclude data on South Lake Tahoe HSA from further analyses, and results presented from the project thus only include 208 HSAs.

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