Covariate Factors

We obtained patient demographic information, including age, gender, race (white, black, Hispanic, Asian/Pacific Islander, or other), number of chronic diseases (0, 1–3, or ≥4), median income quartile of patients' (zip or other). We obtained surgery center information, including urban versus rural location and hospital based versus freestanding ambulatory surgery center. We calculated the volume of procedures performed at each surgical site and determined terciles for low- (≤52 procedures/y), medium- (52–122 procedures/y), and high-volume (≥123 procedures/y) surgery centers. Only Maryland and Florida included data regarding surgeon identifiers, and so, for these states, we also calculated the volume of procedures performed by individual surgeons and determined surgical volume terciles with an equal number of surgeons: low (≤15 procedures/y), medium (16–34 procedures/y) and high (≥35 procedures/y). We also defined a variable for the count of types of sinus procedures performed for each patient discharge.²¹ We defined the number of sinus procedures per case as the count of the sinuses operated on (range, 1–4). The SASD data set does not distinguish between uni- versus bilateral sinus procedures.²¹ For this reason, paired procedures (e.g., bilateral maxillary procedures) were only counted as a single procedure type.