This book came about almost without our realising it. We needed something to give to our undergraduate students who were about to embark on projects that involved measuring behaviour. No single source was concise enough or easily accessible to them, so we prepared some notes. These grew longer and longer, they generated more and more comments and, before long, we found ourselves doing something that neither of us had planned.

As the shape of the book started to emerge, we felt that its recommendations ought to represent, as far as possible, the collective view of the practitioners of the subject, rather than merely our own opinions. Therefore, a draft version was read by a large number of friends and colleagues. The eventual book was immeasurably improved by their advice, comments, criticisms and suggestions. Inevitably, some issues still provoke substantial disagreement; we have attempted to indicate where this is the case and where we have departed from common practice.

Some of our reviewers asked us to put in detailed examples, to illustrate the general points and to show in particular cases how methods are selected and used. We decided not to do so to the extent they would have liked for several reasons. First, we wanted to keep the book as concise as possible, in order to make the information in it readily accessible. Second, we wished to draw attention to general principles of measurement and analysis.