The Dr. Fox effect is the overriding influence of instructor expressiveness on students' evaluations of college/university teaching. This paper contains a reanalysis of data from two studies. A factor analysis of the rating items identified five evaluation factors which varied in the way they were affected by experimental manipulations of instructor expressiveness and content coverage in three incentive conditions. Particularly for students in the incentive condition most like the classroom, the Dr. Fox effect was not supported in that (1) instructor expressiveness only affected ratings of Instructor Enthusiasm--the factor most logically related to the manipulation and (2) content coverage affected ratings of Instructor Knowledge--the factor most logically related to that manipulation--and examination performance, but not ratings of Instructor Enthusiasm. However, when students were not given incentive to learn, instructor expressiveness had a greater impact than did content coverage on each of the student rating factors (supporting the Dr. Fox effect) and examination performance.