This book presents a technique for analyzing the effects of variables, groups, and treatments in both experimental and observational settings. It considers not only the main effects of one variable upon another, but also the effects of group cases.
Not quite as easy to get through as the others in thsi series. one note to the author is perhaps to take a look at how some of the other books in the series wrote the equations (so that all the variables are clearly listed immediately after the equation. This book, kind of does this, but then occassionally does not.
I also think that there are some equation simplifications that can be done in describing least squares. I think instead of A(x,y) - A(mean), it might just be easier to write it in terms of Change in A such that A is distance from mean, then just use the variable. this ends up with less variables and equations that remind you of simple algebra... just my personal opinion.