Introduction: Workplace based assessments (WBAs) are integral to emergency medicine residency training. However many biases undermine their validity, such as an assessor's personal inclination to rate learners leniently or stringently. Outlier assessors produce assessment data that may not reflect the learner's performance. Our emergency department introduced a new Daily Encounter Card (DEC) using entrustability scales in June 2018. Entrustability scales reflect the degree of supervision required for a given task, and are shown to improve assessment reliability and discrimination. It is unclear what effect they will have on assessor stringency/leniency – we hypothesize that they will reduce the number of outlier assessors. We propose a novel, simple method to identify outlying assessors in the setting of WBAs. We also examine the effect of transitioning from a norm-based assessment to an entrustability scale on the population of outlier assessors. Methods: This was a prospective pre-/post-implementation study, including all DECs completed between July 2017 and June 2019 at The Ottawa Hospital Emergency Department. For each phase, we identified outlier assessors as follows: 1. An assessor is a potential outlier if the mean of the scores they awarded was more than two standard deviations away from the mean score of all completed assessments. 2. For each assessor identified in step 1, their learners’ assessment scores were compared to the overall mean of all learners. This ensures that the assessor was not simply awarding outlying scores due to working with outlier learners. Results: 3927 and 3860 assessments were completed by 99 and 116 assessors in the pre- and post-implementation phases respectively. We identified 9 vs 5 outlier assessors (p = 0.16) in the pre- and post-implementation phases. Of these, 6 vs 0 (p = 0.01) were stringent, while 3 vs 5 (p = 0.67) were lenient. One assessor was identified as an outlier (lenient) in both phases. Conclusion: Our proposed method successfully identified outlier assessors, and could be used to identify assessors who might benefit from targeted coaching and feedback on their assessments. The transition to an entrustability scale resulted in a non-significant trend towards fewer outlier assessors. Further work is needed to identify ways to mitigate the effects of rater cognitive biases.