In order to evaluate new educational material the contentment of students with this material is often measured. However, just because a student is contented doesn't mean that he/she has actually learned something. Is there any research investigating the correlation between students contentment and the educational quality of the presented material?
Remark: I just started to get interested in this topic. My starting point is the question, how I can evaluate articles I have written for an online textbook. Is it sufficient to ask the reader whether the article helps him?! So my question is rather broad. I am also interested in research about the correlation between the quality and the number of visitors or the ranking in Google. Also research about the students contentment of a lecture and its quality is fine.