We have had various anecdotal evidence that incentives have limited impact on large scale course evaluations. One piece of this evidence came from a comparison of the College of Agriculture Human and Natural Resource Sciences (CAHNRS) and the College of Engineering and Architecture (CEA). Each organization surveyed ~300 course sections and ~10,000 total enrollments.  CAHNRS allows instructors to offer extra credit if they choose, CEA forbids faculty geting the data that would make offering extra credit possible. CEA offers a drawing for gift certificate. They award 20 at $20 and 2 at $50 each semester. Our observation is that the the response rates in the two colleges vary for complex reasons that do not suggest extra credit is explanatory.

Additionally, CEA has reported that for Spring 2008 only  9 of the 22 awards were picked up by students, despite modifying the procedure to gather the students preferred email address in the drawing, rather than using the university issued email address. The implication is that students are not incented by this level of monetary reward.