How the surgery study was conducted

For this study, Stanford professor Laurence Baker analyzed five years of statewide hospital (and some outpatient) discharge data from the Office of Statewide Health Planning and Development. He focused on 13 medical procedures, including a stroke prevention surgery called carotid endarterectomy.

The data, representing 2005 through 2009, are tied to patient zip codes and reflect where the patients lived, not where they received care. Data from federal facilities, such as VA hospitals, are not included.

Baker broke the data into 24 established medical geographies known as Hospital Referral Regions (HRRs). HRRs are made up of smaller regions called Hospital Service Areas (HSAs), which also were analyzed.

To control for demographic and health differences among the regions, Baker risk adjusted his results for age, sex, race, education, income and health insurance status. In the case of the stroke prevention procedure, he also adjusted for rates of hospitalizations for heart attack and when the patient had a diabetes diagnosis.

He organized his findings into three categories: Rates for people under 65, over 65 and all.

You can find his results for the stroke surgery here.  (Click the tab called Carotid Endarterectomy on the right of the screen.)

The state rate is the baseline, and represents the average rate at which procedures are performed statewide. The state rate, however, is not necessarily the correct rate. It just provides a benchmark against which to compare the regional rates.

Baker’s methodology and results were reviewed by an advisory board made up of 26 physicians and researchers, including Ralph Brindis, immediate past president of the American College of Cardiology, and Rita Redberg, a UCSF cardiologist and editor of the Archives of Internal Medicine.

Here are more details about how Baker conducted his analysis.

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