I would have given it 31/2 stars if that was an option. My main problem with the book was that it was published in 1981, so it is lacking a lot of more recent studies, especially the Minnesota study. The book provided me with exactly what I was looking for though, and that was more detailed examples than the previous books I had read. It is a very detailed book, with plenty of charts and graphs. A more scientifically oriented person would likely appreciate it more. If the book was more current and I hadn't just finished reading 3 other books on the subject, I might have given it a 4 or 5 star rating. I would, however, recommend it for anyone highly interested in this subject.