Here is an informative review of Valen E. Johnson’s book, Grade Inflation: A Crisis in College Education. Johnson is a statistician by training and is now at the University of Texas. The book was published in 2003 and documents a strong relationship between grades and evaluations.
According to the review, “Instructors who grade more stringently are likely to have more students give them lower SET ratings than the instructors who grade less stringently, because they [the students] feel that it is the instructor’s fault that they are earning a lower grade.” Also, “One of the most important conclusions from Johnson’s work is that SET ratings generally don’t measure student learning. Instead, they measure student satisfaction with the teacher. The two are not always related.”