Limitations
This study has several important limitations. First, there may be inaccuracies in classification of endocrinologists and reporting and attribution of the payments in the Open Payments Database and NPPES databases. These errors may have contributed to differences in trends since the Open Payments system was introduced in 2013. Second, there might be financial relationships between physicians and the healthcare industry not covered by the Open Payments Database. For example, information on free medication samples (15,17,18,35) and some small payments (<$100/year) and discounts are not required to be reported. Third, primary specialty is self-declared by each physician so there may be misclassification. Fourth, in relation to the associated research payments, the Open Payments Database has important limitations in the transparency in research payment data and caution should be exercised in interpreting the results. Associated research payments include funding paid to affiliated institutions and are difficult to compare to amounts paid directly to individual physicians. Further, these research payments to teaching hospitals and other institutions where endocrinologists served as principal investigators do not include information about the internal allocation of research payments to physicians, nurses, staff, and research coordinators within the institutions. This is important as the study found that more than 99.9% of associated research payments were assigned to teaching hospitals and other institutions. Finally, as mentioned, the Open Payments Database contains indirect research costs for medications and medical supplies which were provided by the healthcare industry and were used in research sponsored by the public sectors such as NIH. Therefore, the study tabulations cannot discern the amount of research supported by the healthcare industry that was provided to the NIH as industry support for studies in which the named endocrinologists participated.