There are several limitations inherent in this study. Response rates were relatively low and the sample size smaller than ideal, making it difficult to detect smaller effects that may exist. Resident physicians, particularly those at large academic health centers in Boston and Atlanta may differ from physicians who typically make thrombolysis decisions, so it remains to be seen if those with greater experience show the same pattern. Nevertheless, our primary findings are based on an experimental manipulation involving randomized assignment of the physician to a black or white patient vignette, which provides confidence in the causal interpretations that are drawn. A second limitation derives from the use of a computerized presentation of a patient, which may, for reasons that may not be obvious, have contributed to an outcome that may not occur in a typical in-person encounter. The result of predictive validity we report may be an overestimation, but equally likely an underestimation of the role of implicit bias in clinical decision making.
