Student rating myths versus research facts from 1924 to 1988. Reconceptualizing the evaluation of teaching in higher education. Students can make reliable and valid judgements about an instructor and certain aspects of instruction. Just as you would throw away a bathroom scale that gave you a different measure of your weight every time that you stepped on it, an evaluation form with low reliability also should be thrown away. Fortunately, under best case scenarios, student evaluation forms have been shown to be reliable.
Reliability refers to the consistency, stability, and replicability of a measurement.
The consistency of student evaluations refers to the extent that students within the same class give similar ratings on a given question. Good consistency is achievable with class sizes greater than 30. Class sizes of 10 or fewer students will probably not produce adequate consistency. The stability of student evaluations refers to the agreement among raters over time. Student evaluations tend to be fairly stable.