We propose a new framework for optimal experimentation, which we term the “A/B testing problem.” Our model departs from the existing literature by allowing for fat tails. Our key insight is that the optimal strategy depends on whether most gains accrue from typical innovations or from rare, unpredictable large successes. If the tails of the unobserved distribution of innovation quality are not too fat, the standard approach of using a few high-powered “big” experiments is optimal. However, if the distribution is very fat tailed, a “lean” strategy of trying more ideas, each with possibly smaller sample sizes, is preferred. Our theoretical results, along with an empirical analysis of Microsoft Bing’s EXP platform, suggest that simple changes to business practices could increase innovation productivity.

We introduce a new method to measure the temporal discounting of money. Unlike preceding methods, our method requires neither knowledge nor measurement of utility. It is easier to implement, clearer to subjects, and requires fewer measurements than existing methods.

A childhood intervention to improve the social skills and self-control of at-risk kindergarten boys in the 1980s had positive impacts over the life course: higher trust and self-control as adolescents; increased social group membership, education, and reduced criminality as young adults; and increased marriage and employment as adults. Using administrative data, we find this intervention increased average yearly employment income by about 20 percent and decreased average yearly social transfers by almost 40 percent. We estimate that $1 invested in this program around age 8 yields about $11 in benefits by age 39, with an internal rate of return of around 17 percent.

The article discusses several books about various topics. Some of the books are: "Deterring Fraud: The Internal Auditor's Perspective," by W. Steve Albrecht, Ketth R. Howe and Marshall B. Romney, "Management Control in Nonprofit Organizations," 3rd ed., by Robert N. Anthony and David W. Young, "Business Expansion Scheme," by Brian Armitage, "Bank Accounts: A World Guide to Confidentiality," by Edouard Chambost, translated by Peter Walton and Margaret Thompson, "The Tangled Web of Price Variation Accounting: The Development of Ideas Underlying Professional Prescriptions in Six Countries," by F.L. Clarke, "Fore-Runners of Realizable Values Accounting in Financial Reporting," edited by G.W. Dean and M.C. Wells, "Careers in Accounting," by Gloria L. Gaylord and Glenda E. Ried, "Bridges to Infinity: The Human Side of Mathematics," by Michael Guillen, "Bond Duration and Immunization: Early Developments and Recent Contributions," edited by Gabriel A. Hawawini, "Foundations: The Greenwood Encyclopedia of American Institutions," edited Harold M. Keele and Joseph C. Kiger, "The Impact of Taxes on U.S. Citizens Working Abroad," by Ernest R. Larkins.

We use a series of field experiments in rural Burundi to examine the impact of exposure to conflict on social, risk, and time preferences. We find that conflict affects behavior: individuals exposed to violence display more altruistic behavior towards their neighbors, are more risk-seeking, and have higher discount rates. Large adverse shocks can thus alter savings and investments decisions, and potentially have long-run consequences—even if the shocks themselves are temporary.