Re-conceptualising and accounting for examiner (cut-score) stringency in a ‘high frequency, small cohort’ performance test

Variation in examiner stringency is an ongoing problem in many performance settings such as in OSCEs, and usually is conceptualised and measured based on scores/grades examiners award. Under borderline regression, the standard within a station is set using checklist/domain scores and global grades acting in combination. This complexity requires a more nuanced view of what stringency might mean when considering sources of variation of cut-scores in stations. This study uses data from 349 administrations of an 18-station, 36 candidate single circuit OSCE for international medical graduates wanting to practice in the UK (PLAB2). The station-level data was gathered over a 34-month period up to July 2019. Linear mixed models are used to estimate and then separate out examiner (n = 547), station (n = 330) and examination (n = 349) effects on borderline regression cut-scores. Examiners are the largest source of variation in cut-scores accounting for 56% of variance in cut-scores, compared to 6% for stations, < 1% for exam and 37% residual. Aggregating to the exam level tends to ameliorate this effect. For 96% of examinations, a ‘fair’ cut-score, equalising out variation in examiner stringency that candidates experience, is within one standard error of measurement (SEM) of the actual cut-score. The addition of the SEM to produce the final pass mark generally ensures the public is protected from almost all false positives in the examination caused by examiner cut-score stringency acting in candidates’ favour.