Thesis (MComm)--Stellenbosch University, 2012. / As a means to measure job performance, performance appraisal plays a central role in effective individual and organisational management (Behn, 2003). Sound performance management and performance measurement are fundamental to a productive workplace and critical for a high-performing organisation (Jordan, 2002). Performance appraisal research has shifted its emphasis from psychometric issues to the examination of rater cognitive processes and the social and contextual variables which affect performance evaluation. Since raters are important factors in successful performance measurement, one line of research has investigated the effect of similarity, between rater and ratee, on subsequent performance ratings. These studies have mostly relied on similarity measures based on physical similarity characteristics, such as demographic variables. The inconclusive nature of these studies’ findings suggests that the complexity of interpersonal similarity and its effect on ratings has most likely been oversimplified. In the social-cognition literature, substantial evidence exists that rater-ratee acquaintance shifts the focus of similarity judgment to “deeper”, sometimes unobservable, characteristics, like values, motives and attitudes. This research study investigates whether rater-ratee similarity in Big Five personality traits unduly influences task-orientated performance ratings. Self-report personality data (IPIP; Goldberg, 2006) were collected from university lecturers and their students (N = 152). Actual lecturer task performance assessment data (end-of-semester student feedback ratings) were gathered concurrently. Data were analysed through polynomial regression analysis and response surface methodology. Results indicated that ratee (i.e., lecturer) extraversion (r = .357), conscientiousness (r = .413) and openness (r = .178) had significant main effects on average performance ratings. Also, rater-ratee personality similarity in extraversion (p < .001), neuroticism (p < .01) and openness (p < .001) had a significant effect on performance ratings, with the effects of agreeableness and conscientiousness also approaching significance. The present study further extends earlier research by using task performance ratings as criterion measures — as opposed to earlier studies that used contextual performance ratings — and also used “upward” ratings of seniors, instead of peer- or ‘downward’ ratings of performance, as was done in earlier studies of personality similarity effects. The results suggest that (a) earlier conclusions that personality similarity does not affect performance ratings seem to be premature, (b) more research is needed to investigate why personality similarity affects ratings and last, (c) we do not yet understand the boundary conditions that affect this phenomenon.