The intent of this book is to introduce researchers in health sciences to these concepts of measurement. It is not an introductory textbook, in that we do not confine ourselves to a discussion of introductory principles and methods; rather, we attempt to make the book as current and comprehensive as possible. The book does not delve as heavily into mathematics as many books in the field, such side trips may provide some intellectual rewards for those so inclined, but frequently at the expense of losing the majority of readers. Similarly, we emphasize applications, rather than theory, so that some theoretical subjects (like Thurstone's Law of Comparative Judgement) which are of historical interest but little practical importance, are omitted. Nevertheless, we spend considerable time in explanation of the concepts underlying current approaches to measurement. One other departure from current books is that our focus is on those attributes interest to researchers in health sciences-subjective states, attitudes response to illess, etc. rather than the topics such as personality or achievement familiar to readers in education and psychology. As a result, our examples are drawn from the literature in health sciences