The Rationality Quotient

The Rationality Quotient

Toward a Test of Rational Thinking

By Keith E. Stanovich, Richard F. West and Maggie E. Toplak

How to assess critical aspects of cognitive functioning that are not measured by IQ tests: rational thinking skills.





How to assess critical aspects of cognitive functioning that are not measured by IQ tests: rational thinking skills.

Why are we surprised when smart people act foolishly? Smart people do foolish things all the time. Misjudgments and bad decisions by highly educated bankers and money managers, for example, brought us the financial crisis of 2008. Smart people do foolish things because intelligence is not the same as the capacity for rational thinking. The Rationality Quotient explains that these two traits, often (and incorrectly) thought of as one, refer to different cognitive functions. The standard IQ test, the authors argue, doesn't measure any of the broad components of rationality—adaptive responding, good judgment, and good decision making.

The authors show that rational thinking, like intelligence, is a measurable cognitive competence. Drawing on theoretical work and empirical research from the last two decades, they present the first prototype for an assessment of rational thinking analogous to the IQ test: the CART (Comprehensive Assessment of Rational Thinking).

The authors describe the theoretical underpinnings of the CART, distinguishing the algorithmic mind from the reflective mind. They discuss the logic of the tasks used to measure cognitive biases, and they develop a unique typology of thinking errors. The Rationality Quotient explains the components of rational thought assessed by the CART, including probabilistic and scientific reasoning; the avoidance of “miserly” information processing; and the knowledge structures needed for rational thinking. Finally, the authors discuss studies of the CART and the social and practical implications of such a test. An appendix offers sample items from the test.


$40.00 X ISBN: 9780262034845 480 pp. | 6 in x 9 in 14 line drawings


$35.00 X ISBN: 9780262535274 480 pp. | 6 in x 9 in 14 line drawings


  • The Rationality Quotient is a significant advance in the psychology of rationality. It presents the best analysis of cognitive errors in the scientific literature and makes a compelling case for measuring rationality independently of intelligence.

    Daniel Kahneman

    Princeton University; winner of the 2002 Nobel Prize in Economics

  • The project presented by these authors is staggering in its scale and ambition. This work greatly advances our understanding of the distinction between IQ and rational thinking measures over a wide range of cognitive tasks. It also lays the foundation for a test of rational thinking that includes the essential elements missed by IQ testing. This book is essential reading for educationalists, psychometricians, and cognitive psychologists alike.

    Jonathan Evans

    Emeritus Professor of Cognitive Psychology, University of Plymouth

  • Trying to determine if The Rationality Quotient was suitable for my graduate seminar, I realized I was totally immersed in the case being argued. The book has the happy quality of being novel, yet synthesizing a respected research tradition. These authors are first-rate scholars and they have produced an unusually erudite work. In the end, I determined it is highly suitable for my seminar, but it is also excellent for less advanced audiences because of its clear and careful exposition.

    Stephen J. Ceci

    Helen L. Carr Professor of Developmental Psychology, Cornell University

  • This groundbreaking book is the culmination of decades of research on what it means to be rational. Previously, these authors argued that being smart (in the IQ sense) does not mean being rational. In this book, they develop a measure that is to rationality what the IQ test is to intelligence. Rationality, as measured by the CART, is a multidimensional concept that embodies the ability, the inclination, and the knowledge to make good decisions. Meticulously tested with over 4,000 participants, the result is the first genuine 'gold standard' of rational thinking. A monumental achievement and a must-read for all who call themselves scholars of reasoning.

    Valerie Thompson

    Professor of Psychology, University of Saskatchewan; editor of the journal Thinking & Reasoning

  • This volume profoundly challenges the century-old citadel of psychometric intelligence, reconceiving what it is to be smart with a measure of rationality richly grounded in contemporary cognitive science's dual-process model.

    David N. Perkins

    Carl H. Pforzheimer Jr. Research Professor of Teaching and Learning, Harvard Graduate School of Education


  • Winner, 2017 PROSE Awards, Education Theory category