First we explored the factor structure (Principal Component Analysis) and the reliability (Cronbach alpha) of the two components of presentation skills, ‘content’ and ‘delivery’. We conducted a one-way analysis of variance (ANOVA) and computed the amount of explained variance (Eta2) in the evaluation scores accounted for by the factors ‘assessee’, ‘assessor’ and ‘group’. We expected that a substantial amount of variance could be explained by the factor ‘assessee’ and that this amount of variance is larger than the variance explained by the factor ‘assessor’. Such a result is a prerequisite to accept the validity of the instrument and assessment approach when studying differences in the mastery of presentation skills. The amount of variance explained by the factor ‘assessor’, on the other hand, can also be considered as indicator for the amount of influence assessors characteristics have on the scores. In that case it is important to find out which characteristics of the assessor are responsible for assessor bias