51¹ú²úÊÓƵ

The student satisfaction survey will be invalid not only because responders differ in opinion from non-responders, but also because the agree/disagree boxes are flawed. The array of five boxes elicits an abnormally high proportion of responses in the middle box, which means no opinion at all. That leaves only extreme opinions from an unrepresentative minority.

David Booth
School of Psychology
51¹ú²úÊÓƵ of Birmingham