Statistical analyses
Descriptive analyses were performed on payment data. Per-physician payments were calculated only among endocrinologists receiving payments each year, as in previous studies (20-22). Regarding general payments, this study performed descriptive analyses, including calculation of per-physician payments and total amounts, for general payments excluding ownership interests and royalties and licenses (hereby GPEOR), because only several endocrinologists received large amounts of ownership interests and royalties and licenses (Supplemental Material 3). For associated research payments, per-physician payments were calculated as total payments divided by the number of principal investigators in a research payment, and total research payments were calculated by the number of endocrinologists times the payment per principal investigator because some research payments included principal investigators with other specialties. The author evaluated the share of payments by specific proportions of endocrinologists and the Gini index. The Gini index ranges from 0 (complete equality) to 1 (complete inequality) (21,23). Payment data were also analyzed by categories (20,24,25).
The study evaluated trends in GPEOR and research payments with interrupted time series analysis, using generalized estimating equations (GEE) of annual per-physician payment clustering individual endocrinologists, to adjust for the COVID-19 pandemic’s influence since 2020. As the payment distribution was skewed, the study employed the negative binomial regression GEE model for changes in per-physician payments and modified linear regression GEE model with Poisson distribution for changes in the proportion of endocrinologists receiving payments from 2014-2022 (22,23,25,26). Relative annual mean percentage change was reported. The study excluded from the GEE trend analyses of GPEOR those payments for acquisitions, debt forgiveness, and long-term medical supply or device loans, because general payments for acquisitions, debt forgiveness, and long-term medical supply or device loans were only available for 2021-2021 data. Inflation was adjusted to 2022-dollar values by dividing the payment values each year by relative consumer price index (CPI) compared to 2022 from the US Bureau of Labor Statistics CPI Inflation Calculator (Supplemental Material 4).