Which Researchers Listed Below Did Not Complete an Empirical Study

Which researchers listed below did not complete an empirical study that revealed disparate physician and patient communications by subgroups:

A) Siminoff, Graham and Gordon (2006)
B) Kelly and Haidet (2007)
C) Street, et al. (2009)
D) a, b and c's research did not involve physician and patient communications as a source of disparate healthcare
E) a, b, and c did involve physician and patient communication. Therefore, not a single study cited, "…did not" address disparate physician/patient communication