Volume-accumulated experience over running six-month windows involved recording surgeons’ volume at a given date as the number of procedures accumulated during the prior six months. selleck chemical This measure is more precise than fixed calendar periods and was used extensively in the literature, as it responds instantaneously to any changes in the surgeon’s recent experience profile. Experience accumulation with moving, rather than fixed, windows can be viewed as smoothing the calendar step function and alleviating the imprecision that increases for observations occurring toward the end of the observation period [29]. 2.4. Statistical Analyses Initial counts, percentages, means, and standard deviations for patient demographics, comorbid conditions, hospital characteristics, as well as safety utilization and cost outcomes were summarized separately for VATS lobectomy versus VATS wedge resection and separately for thoracic surgeons versus all surgeons using descriptive statistics.

Type of surgeon (thoracic versus general) was identified via physician identification codes provided in the database. The safety outcomes of interest were pertinent adverse events occurring during or up to 30�C60 days after surgery. A dichotomous variable was used indicating the existence of an adverse event as well as a continuous variable tallying the number of adverse events. Utilization outcomes were surgery duration (hours) and hospital length of stay (days). Cost outcomes were total hospital costs per patient, both fixed and variable. Since we only studied VATS procedures, we did not include costs for initial acquisition of the VATS equipment.

In addition, descriptive statistics for the volume explanatory variables are presented. The key explanatory variable was each surgeon’s volume for lobectomy and wedge resection using VATS or open thoracotomy techniques. This measure of volume corresponded to the aggregate experience level of the surgeon over running six-month windows. Experience with open thoracotomy procedures may or may not contribute to performance with VATS, but it is certainly expected that experience specific to VATS will be Cilengitide the most relevant in explaining outcomes for patients treated with VATS. Multivariable logistic regression analyses were estimated for the adverse event binary outcome: the presence or absence of specific individual events. Ordinary least squares (OLS) regression was used for all other continuous outcomes such as hospital costs, surgery time, length of stay, and number of adverse events. For all models, in addition to the volume measures, the following explanatory variables were included: age, gender, race, marital status, insurance type, diagnosis (metastasis versus primary cancer), comorbid conditions (e.g.