Thyroid nodule has been a common and serious threaten to human health. With the identification and diagnosis of thyroid nodules in the general population, large volumes of examination reports in clinical practice have been accumulated. They provide data basics of analyzing radiologists' behavior of diagnosing thyroid nodules. To conduct data-driven analysis of radiologists' behavior, an experimental framework is designed based on belief rule base, which is essentially a white box for knowledge representation and uncertain reasoning. Under the framework, with 2744 examination reports of thyroid nodules in the period from January 2012 to February 2019 that have been collected from a tertiary hospital located in Hefei, Anhui, China, experimental results are obtained from conducting missing validation, self-validation, and mutual validation. Three principles are then concluded from the results and corresponding analysis. The first is that missing features on some criteria are considered as benign ones by default, the second is that there is generally inconsistency between the recorded features on criteria and the overall diagnosis, and the third is that different radiologists have different diagnostic preferences. These three principles reflect three diagnostic behavioral characteristics of radiologists, namely reliability, inconsistency, and independence. Based on the three principles and radiologists' behavioral characteristics, managerial insights in a general case are concluded to make the findings in this study available in other situations.