Daniel Kahneman Princeton University

Experiences of Collaborative Research Daniel Kahneman Princeton University The author’s personal history of the research that led to his I spent the summer of 1969 doing research at the recognition in economics is described, focusing on the Applied Psychological Research Unit in Cambridge, En- process of collaboration and on the experience of contro- gland. Amos stopped there for a few days on his way to the versy. The author’s collaboration with Amos Tversky dealt United States. I had drafted a questionnaire on intuitions with 3 major topics: judgment under uncertainty, decision about sampling variability and statistical power, which was making, and framing effects. A subsequent collaboration, based largely on my personal experiences of incorrect with the economist Richard Thaler, played a role in the research planning and unsuccessful replications. The ques- development of behavioral economics. Procedures to make tionnaire consisted of a set of problems, each of which controversies more productive and constructive are could stand on its own, making its own point—I had long suggested. had the ambition of doing “psychology with single questions,” and this was an opportunity to try it. Amos went off The Collaboration With Amos Tversky and administered the questionnaire to participants at a meeting of the Mathematical Psychology Association, and t was the spring of 1969, and I was teaching a graduate a few weeks later, we met in Jerusalem to look at the results seminar at the Hebrew University of Jerusalem on the and write a paper. applications of psychology to real-world problems. In The experience was magical. I had enjoyed collabo- I rative work before, but this was different. Amos was often what turned out to be a life-changing event, I asked my younger colleague Amos Tversky to tell the class about described by people who knew him as the smartest person what was going on in his field of judgment and decision they knew. He was also very funny, with an endless supply making. Amos told us about the work of his former mentor, of jokes appropriate to every nuance of a situation. In his Ward Edwards, whose lab was using a research paradigm presence, I became funny as well, and the result was that in which participants were shown two book bags filled with we could spend hours of solid work in continuous mirth. poker chips. The bags were said to differ in their composition The paper we wrote was deliberately humorous—we de- (e.g., 70 red and 30 white chips or 30 red and 70 white chips). scribed a prevalent belief in the “law of small numbers,” One bag was randomly chosen. The participant was given an according to which the law of large numbers extends to opportunity to sample successively from it and was required small numbers as well. Although we never wrote another to indicate after each trial the probability that it came from the humorous paper, we continued to find amusement in our predominantly red bag. Edwards had concluded from the work—I have probably shared more than half of the laughs results that people are conservative Bayesians: They almost of my life with Amos. always adjust their confidence interval in the proper direction, And we were not just having fun. I quickly discovered but rarely far enough. that Amos had a remedy for everything I found difficult A lively discussion developed around Amos’s talk. about writing. With him, movement was always forward. The idea that people were conservative Bayesians did not Progress might be slow, but each successive draft we seem to fit with the everyday observation of people com- produced was an improvement—this was not something I monly jumping to conclusions. It also appeared unlikely could take for granted when working on my own. Amos’s that the results obtained in the sequential sampling para- work was always characterized by confidence and by a digm would extend to the situation, arguably more typical, crisp elegance, and it was a joy to find those characteristics in which evidence is delivered all at once. Finally, the label now attached to my ideas as well. As we were writing our conservative Bayesian suggested a process that first gets first paper, I was conscious of how much better it was than the correct answer, then adulterates it with a bias—not a the more hesitant piece I would have written by myself. I plausible psychological mechanism. I learned recently that one of Amos’s friends met him that day and heard about our conversation, which Amos described as having se- Editor’s note. This excerpt was adapted with permission from a longer verely shaken his faith in the neo-Bayesian approach. autobiographical statement to be published in Les Prix Nobel 2002 (Fra¨ngsmyr, in press). Copyright by the Nobel Foundation. Adapted by Amos and I decided to meet for lunch to discuss our permission. hunches about the manner in which probabilities are “re- ally” judged. There we exchanged personal accounts of our Author’s note. Correspondence concerning this article should be ad- own recurrent errors of judgment in this domain and de- dressed to Daniel Kahneman, Department of Psychology, Princeton Uni- cided to study the statistical intuitions of experts. versity, Princeton, NJ 08544-1010. E-mail: [email protected] September 2003 ● American Psychologist 723 Copyright 2003 by the American Psychological Association, Inc. 0003-066X/03/$12.00 Vol. 58, No. 9, 723–730 DOI: 10.1037/0003-066X.58.9.723 thought. Some of the greatest joys of our collaboration— and probably much of its success—came from our ability to elaborate each other’s nascent thoughts: If I expressed a half-formed idea, I knew that Amos would be there to understand it, probably more clearly than I did, and that if it had merit, he would see it. Like most people, I am somewhat cautious about exposing tentative thoughts to others—I must first make sure that they are not idiotic. In our years of close collaboration, this caution was com- pletely absent. The mutual trust and the complete lack of defensiveness that we achieved were particularly remark- able because both of us—Amos even more than I—were known to be severe critics. Our magic worked only when we were by ourselves. We soon learned that joint collaboration with any third party should be avoided because we became competitive in a threesome. Amos and I shared the wonder of together owning a goose that could lay golden eggs—a joint mind that was better than our separate minds. The statistical record con- Amos Tversky firms that our joint work was superior, or at least more Photo by Ed Souza, influential, than the work we did individually (Laibson & Stanford News Service Zeckhauser, 1998). Amos and I published eight journal articles during our peak years (1971–1981), of which five had been cited more than a thousand times by the end of 2002. Of our separate works, which in total number over don’t know exactly what it was that Amos found to like in 200, only Amos’s theory of similarity (Tversky, 1977) and our collaboration—we were not in the habit of trading my book on attention (Kahneman, 1973) exceeded that compliments—but clearly he was also having a good time. threshold. We were a team, and we remained in that mode for well The special style of our collaborative work was rec- over a decade. The Nobel Prize was awarded for work that ognized early by a referee of our first theoretical paper (on we produced during that period of intense collaboration. representativeness), who caused it to be rejected by Psy- At the beginning of our collaboration, we quickly chological Review. The eminent psychologist who wrote established a rhythm that we maintained during all our that review—his anonymity was betrayed years later— years together. Amos was a night person, and I was a pointed out that he was familiar with the separate lines of morning person. This made it natural for us to meet for work that Amos and I had been pursuing and considered lunch and a long afternoon together and still have time to both quite respectable. However, he added the unusual do our separate things. We spent hours each day just remark that we seemed to bring out the worst in each other talking. We did almost all the work on our joint projects and certainly should not collaborate. He found most objec- while physically together, including the drafting of ques- tionable our method of using multiple single questions as tionnaires and papers, and we avoided any explicit division evidence—and he was quite wrong there as well. of labor. Our principle was to discuss every disagreement until it had been resolved to our mutual satisfaction, and we The 1974 Science Article and the had tie breaking rules for only two topics: whether an item Rationality Debate should be included in the list of references (Amos had the casting vote) and who should resolve any issue of English Amos and I were at the Oregon Research Institute (ORI) in grammar (my dominion). We did not initially have a con- Eugene from 1971 to 1972, a year that was by far the most cept of a senior author. We tossed a coin to determine the productive of my life. We did a considerable amount of order of authorship of our first paper and alternated from research and writing on the availability heuristic, on the then on until the pattern of our collaboration changed in the psychology of prediction, and on the phenomena of an- 1980s.

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