This is the largest Navitoclax Phase 2 all-payer inpatient database in the U.S., with records from approximately eight million hospital stays each year. Records were limited to adults aged 18�C100 years old hospitalized with a diagnosis of cholecystitis, as identified by ICD-9 codes and Clinical Classifications Software (CCS). ICD-9 procedure codes were used to identify all patients who underwent cholecystectomy as the primary procedure during hospitalization (open versus laparoscopic). Patients were stratified into four age groups, aged 18�C49, 50�C64, 65�C79, and ��80 years. Patient comorbidity was calculated using ICD-9 codes and the Charlson Comorbidity Index. 2.1. Independent Variables Type of procedure (open versus laparoscopic cholecystectomy) was the primary independent variable of interest.

For this study, only those patients who carried a diagnosis of cholecystitis and had cholecystectomy as the primary procedure performed during that hospitalization were included. 2.2. Outcome Variables The primary outcome examined was rate of laparoscopic cholecystectomy by year and age group. Outcomes by type of cholecystectomy (open versus laparoscopic) examined were mortality; in-hospital complications; discharge disposition (routine discharge to home versus discharge with home health care or discharge to a short-term hospital, intermediate care facility, or skilled nursing facility), mean length of stay (LOS); and mean total inpatient hospital costs. Surgical complications were identified using ICD-9 codes and categorized as cardiac, postoperative shock, gastrointestinal, hematologic, renal, pulmonary, infection, thrombosis or embolism, and bile duct injury or repair.

Surgical complications were treated as dichotomous variables (none versus ��1). Mean total inpatient hospital costs were calculated using the HCUP-NIS hospital-specific cost-to-charge ratios (available for 2001�C2006) and were standardized to 2006 dollars utilizing the Bureau of Labor Statistics Medical Consumer Price Index [5]. The NIS charge information represents the amount that hospitals were billed for services but does not reflect the actual amount hospital services cost or the specific amounts that hospitals received in payment. In order to see how much to calculate how the hospital charges translate into actual costs, the NIS Cost-to-Charge Ratio Files in the database enable this conversion.

Each file contains hospital-specific cost-to-charge ratios based on all-payer inpatient Entinostat cost for each hospital in the corresponding NIS databases. For this study, cost information was obtained by the NIS database from the hospital accounting reports collected by the Centers for Medicare and Medicaid Services and merged with the appropriate file to the corresponding NIS databases by the data element hospital identification number.