The textbook contains an abundance of footnotes and remarks. They are intended for statistically sophisticated readers who wish to pursue the subject matter in greater depth, and it is not necessary that a novice studying the text for the first time read them. They often expand and elaborate on a particular topic, point the way to generalization and to other techniques, and make historical comments and remarks. In addition, they contain literature citations for further exploration of the topic and refer to finer points of theory and methods. We are confident that this two-tier approach will be pedagogically appealing and useful to readers with a higher degree of scholarly interest.