There is increasing pressure in veterinary education to teach and assess communication skills, with the Objective Structured Clinical Examination (OSCE) being the most common assessment method. Previous research reveals that raters are a large source of variance in OSCEs. This study focused on examining the effect of raters' professional background as a source of variance when assessing students' communication skills. Twenty-three raters were categorized according to their professional background: clinical sciences (n=11), basic sciences (n=4), clinical communication (n=5), or hospital administrator/clinical skills technicians (n=3). Raters from each professional background were assigned to the same station and assessed the same students during two four-station OSCEs. Students were in year 2 of their pre-clinical program. Repeated-measures ANOVA results showed that OSCE scores awarded by the rater groups differed significantly: (F(matched_station_1) [2,91]=6.97, p=.002), (F(matched_station_2) [3,90]=13.95, p=.001), (F(matched_station_3) [3,90]=8.76, p=.001), and ((Fmatched_station_4) [2,91]=30.60, p=.001). A significant time effect between the two OSCEs was calculated for matched stations 1, 2, and 4, indicating improved student performances. Raters with a clinical communication skills background assigned scores that were significantly lower compared to the other rater groups. Analysis of written feedback provided by the clinical sciences raters showed that they were influenced by the students' clinical knowledge of the case and that they did not rely solely on the communication checklist items. This study shows that it is important to consider rater background both in recruitment and training programs for communication skills' assessment.
Keywords: OSCE; communication skills; rater bias; rater effect; veterinary medicine.