Validity of students' evaluations of teaching: Biasing effects of likability and prior subject interest

This study examined the validity of students' evaluations of teaching as an instrument for measuring teaching quality by examining the effects of likability and prior subject interest as potential biasing effects, measured at the beginning of the course and at the time of evaluation. University students (N = 260) evaluated psychology courses in one semester at a German university with a standardized questionnaire, yielding 517 data points. Cross-classified multilevel analyses revealed fixed effects of likability at both times of measurement and fixed effects of prior subject interest measured at the beginning of the course. Likability seems to exert a substantial bias on student evaluations of teaching, albeit one that is overestimated when measured at the time of evaluation. In contrast, prior subject interest seems to introduce a weak bias. Considering that likability bears no conceptual relationship to teaching quality, these findings point to a compromised validity of students' evaluations of teaching.