Are the results for Web-based course evaluations biased?

No, the results are not biased. The evaluation method does not affect the results and students with a strong opinion of the instructor are not more likely to participate. It is safe to assume that when variation occurs, it is caused by some other factor, not the Web-based method of evaluation. Research studies and pilot programs can be designed to reduce variation and increase the overall reliability of the data, but these strategies are appropriate for any comparison of evaluation methods, not only those involving Web-based evaluations.