Frontispiece by Ruth Weisberg FOUNDATIONS OF MEASUREMENT DAVID H. KRANTZ R. DUNCAN LUCE UNIVERSITY OF MICHIGAN THE INSTITUTE FOR ADVANCED STUDY PATRICK SUPPES AMOS TVERSKY STANFORD UNIVERSITY THE HEBREW UNIVERSITY OF JERUSALEM VOLUME I Additive and Polynomial Representations ACADEMIC PRESS, INC. Harcourt Brace Jovanovich, Publishers San Diego New York Berkeley Boston London Sydney Tokyo Toronto COPYRIGHT © 1971, BY ACADEMIC PRESS, INC. ALL RIGHTS RESERVED NO PART OF THIS BOOK MAY BE REPRODUCED IN ANY FORM, BY PHOTOSTAT, MICROFILM, RETRIEVAL SYSTEM, OR ANY OTHER MEANS, WITHOUT WRITTEN PERMISSION FROM THE PUBLISHERS. ACADEMIC PRESS, INC. 1250 Sixth Avenue, San Diego, California 92101 United Kingdom Edition published by ACADEMIC PRESS, INC. (LONDON) LTD. 24/28 Oval Road, London NW1 7DD LIBRARY OF CONGRESS CATALOG CARD NUMBER: 72-154365 ISBN 0-12-425401-2 PRINTED IN THE UNITED STATES OF AMERICA 88 89 90 91 92 10 9 8 7 6 5 4 3 2 The quotation on the opposite page is taken from Plato's Protagoras in The Dialogues of Plato translated by Benjamin Jowett, 4th ed., 1953, Vol. 1, pp. 183-184. Copyright 1953 by the Clarendon Press, Oxford. ... What measure is there of the relations of pleasure to pain other than excess and defect, which means that they become greater and smaller, and more and fewer, and differ in degree? For if any one says: "Yes, Socrates, but immediate pleasure differs widely from future pleasure and pain"—to that I should reply: And do they differ in any- thing but pleasure and pain ? There can be no other measure of them. And do you, like a skillful weigher, put into the balance the pleasures and the pains, and their nearness and distance, and weigh them, and then say which outweighs the other. If you weigh pleasures against pleasures, you of course take the more and greater; or if you weigh pains against pains, you take the fewer and the less; or if pleasures against pains, then you choose that course of action in which the painful is exceeded by the pleasant, whether the distant by the near or the near by the distant; and you avoid that course of action in which the pleasant is exceeded by the painful. Would you not admit, my friends, that this is true? ... Summary of Contents Preface xvii 1. Introduction 1 2. Construction of Numerical Functions 38 3. Extensive Measurement 71 4. Difference Measurement 136 5. Probability Representations 199 6. Additive Conjoint Measurement 245 7. Polynomial Conjoint Measurement 316 8. Conditional Expected Utility 369 9. Measurement Inequalities 423 10. Dimensional Analysis and Numerical Laws 454 Answers and Hints to Selected Exercises 545 References 551 Author Index 565 Subject Index 570 vi Preface Scattered about the literatures of economics, mathematics, philosophy, physics, psychology, and statistics are axiom systems and theorems that are intended to explain why some attributes of objects, substances, and events can reasonably be represented numerically. These results constitute the mathematical foundations of measurement. Although such systems are of some mathematical interest, they warrant our attention primarily as em- pirical theories—as attempts to formulate properties that are observed to be true about certain qualitative attributes. Some of the theories appropriate to classical physics are so well accepted that they are usually considered in the province of philosophy rather than physics, but this should not be allowed to becloud the basic empirical character of any theory that purports, for example, to justify treating mass as an additive numerical property. From time to time, the empirical nature of basic measurement assumptions is forcibly brought to everyone's attention—for example, when the theory of relativity made clear that velocities do not combine additively; when quantum mechanics made clear that the probability theory of elementary particles is somewhat different from that appropriate to macroscopic events; and when we recall that the attribute of hardness still lacks any satisfactory measurement analysis. In the nonphysical sciences, measurement has always been problematic, and it has become increasingly evident to nearly everyone concerned that we must devise theories somewhat different from those that have worked XVll XV111 PREFACE in physics. Because of the active—and we believe crucial—concern with measurement in these sciences, it is not terribly surprising that four behavioral scientists might attempt to summarize the field. The methodology of measure- ment has, of course, a long history in the physical sciences, and we have also tried to cover the major foundational problems there, ranging from the theory of extensive measurement to dimensional analysis. We must emphasize that this book deals with Foundations and not with the history or current practice of measurement in any field. To the extent that we deal with empirical examples, it is to motivate theories and to illustrate their testing. The reader who is interested in specific empirical material will have to consult references in particular specialties. For example, an excellent history of weight measurement, with many illustrations of apparatus, is the volume by Kisch (1965). As one explores the measurement literature it becomes clear that, in spite of the fact that each proof makes some peculiar use of the structure in ques- tion, many proofs are quite similar. Moreover, little is done to relate the particular theorem being presented to any others except those having exactly the same primitive concepts. Eventually, this becomes frustrating: results are reproved ; it is extremely difficult to maintain a clear idea of the structure of the field; it is uncertain how many really basic ideas there are; and it is likely that the field gradually becomes inefficient in the sense that, for about the same effort, stronger theorems could be proved if other results were used instead of returning to first principles. We have attempted to organize the central results in a cumulative fashion. As a result of our attempt, we have concluded that at present there are three distinct mathematical results (see Chapters 1 and 2) used to construct numerical representations of qualitative structures. With some minor exceptions, the remaining major theorems of this volume either reduce to one of these results directly or indirectly via some other representation theorem. By "reduce" we do not mean to suggest "reduce readily," for in many cases the proofs are quite lengthy and it is not always immediately obvious what to reduce to what. In organizing the material, we have un- doubtedly made some arbitrary decisions about this, although as a matter of fact we suspect that there maybe rather less flexibility than might first seem. In the process, we have usually arrived at theorems somewhat better than those previously published, and virtually all of our proofs of major results are different from those in the literature. (Some of our new results have been published independently of this book; any paper on measurement by the authors dated 1967-1970 is a byproduct of work on the book.) Since the book includes both new results and new proofs it is a research monograph, but we hope that it is more than that. We have gone to pains to make it a textbook—in fact, two textbooks. If one deletes Chapter 2 and PREFACE XIX all of the sections headed "Proofs," what remains is a self-contained book that should serve as a comprehensive introduction to the mathematical theory of measurement for nonspecialists who have enough mathematics to understand the formulation of the problems (see below), but who have no particular reason for studying the proofs. For those with the requisite mathematical background, the proofs are there in separate sections. Rather more detail is provided than a trained mathematician is likely to want, but with his facility at skipping things that are routine to reconstruct, this should not really bother him. For the novice, the detail is important because he must learn to develop complete proofs, even though he may ultimately present them only in abbreviated form. The reason is that, more than in some areas of mathematics, it is all too easy to accept and use, as if it were proved, a familiar property that has not been proved and may, given the axioms, be exceedingly tricky or tedious to establish. The most "obvious" properties can be major stumbling blocks or the source of erroneous proofs. To further the usefulness of the book as a text, we have included a number of problems which the student can use to exercise and test his developing skills. Many of these exercises are quite easy for a person familiar with the area, but a few are moderately difficult. In addition, a number of unsolved problems are mentioned throughout the book. Some of these are difficult and are suitable for dissertations; others, no doubt, will turn out to be easier than we have thought. The material that we have elected to cover and our mode of presentation make it impossible to package it conveniently in a single volume. This first volume covers all of the major representation theorems in which the qualitative structure is reflected as some sort of a polynomial function of one or more numerical functions defined on the basic entities. The simplest and best-known examples are additive expressions of a single measure, such as the probability of disjoint events being the sum of their probabilities, and additive expressions of two measures, such as the logarithm of momentum being the sum of log mass and log velocity terms. The second volume will include representations in terms of distances in some sort of space, a treat- ment of the exceedingly perplexing problems raised by errors of measurement, and analyses of the philosophical issues that center about axiomatizability and meaningfulness. Mathematical Background For a reader who plans to skip proofs, a modest background in mathe- matics and some diligence should suffice. He certainly must know well the elementary material on sets, relations, functions, and probability that is provided in introductory courses at many colleges and universities and is XX PREFACE found in, among other books, Kershner and Wilcox (1950) and Suppes (1957). With no more than that, there will be some difficult spots and a few sections will be unintelligible because they depend upon calculus or topological concepts. For the reader who plans to follow the proofs, a background in calculus and in elementary abstract algebra is needed. In a few places, some elementary topological material that can be found in, for example, Kelley (1955) and some of the functional equations found in Aczél (1966) are also required. Selecting Among the Chapters Within the present volume, various courses of study are possible by selecting among the chapters. The main constraints are conceptual de- pendencies and the logical development of the proofs. These two are dia- grammed separately in Figure A. Obviously, many more options are avail- Conceptual Logical (a) (b) FIGURE A. (a) Conceptual dependencies of chapters, (b) Logical development of the proofs. able to those who do not plan to read proofs, and so it may be useful for us to state what we believe to be the minimum core of information for physical and behavioral scientists. A physical scientist who plans to ignore proofs should cover Chapters 1, 3, 6, and 10; he will find that the initial sections of Chapters 4, 5, and parts of Chapter 9 are also valuable. To follow the proofs, Chapter 2 must be added. For a behavioral scientist, the essential chapters are 1, 4, 5, 6, 8, and 9, with Chapter 3 also being desirable. To follow the proofs, Chapters 2 and 3 must be added. In addition, to guide the reader further we have marked with a square (□) those sections of Chapters 3-10 that we consider to be the basic core material. Acknowledgments Each of us has received substantial assistance while working on this book and we gratefully acknowledge it. Krantz: Grants GB-4947 and 8181 from the National Science Foundation to the Univer- sity of Michigan; Public Health Service Special Postdoctoral Fellowship, 1968; and the hospitality of the Center for Advanced Study in the Behavioral Sciences, Stanford, Cali- fornia, during the summer of 1967 and all of 1970-1971. Luce: Grant GB-6536 from the National Science Foundation to the University of Pennsylvania; a National Science Foundation Senior Postdoctoral Fellowship, 1966-1967, which with a sabbatical leave from the University of Pennsylvania permitted him to spend that academic year at the Center for Advanced Study in the Behavioral Sciences, Stanford, California; an Organization of American States Professorship for the academic year 1968-1969 at the Pontificia Universidade Catolica do Rio de Janeiro, Brazil; and a grant from the Alfred P. Sloan Foundation to The Institute for Advanced Study, Princeton, New Jersey. Suppes: Grant GJ-443X from the National Science Foundation to Stanford University. Tversky: Grant GB-6782 from the National Science Foundation to the University of Michigan and the hospitality of the Center for Advanced Study in the Behavioral Sciences, Stanford, California, during the summer of 1967 and all of 1970-1971. Drafts of the chapters have been circulated among a small group of people whom we know to be especially interested in these matters. We have benefited greatly from their comments, some of which have been detailed and penetrating. We thank: J. Aczél, Maya Bar-Hillel, R. L. Causey, R. M. Dawes, Z. Domotor, P. C. Fishburn, R. Giles, E. W. Holman, M. V. Levine, K. R. MacCrimmon, A. A. J. Marley, F. S. Roberts, R. J. Titiev, J. W. Tukey, and T. S. Wallsten. XXI