Katherine L. Milkman

Angela Duckworth, Ahra Ko, Katherine L. Milkman, Joseph S. Kay, Eugen Dimant, Dena Gromet, Aden Halpern, Youngwoo Jung, Madeline K. Paxson, Ramon A. Silvera Zumaran, Ron Berman, Ilana Brody, Colin Camerer, Elizabeth Canning, Hengchen Dai, Marcos Gallo, Hal E. Hershfield, Matthew Hilchey, Ariel Kalil, Kathryn Kroeper, Amy Lyon, Benjamin Manning, Nina Mazar, Michelle Michelini, Susan Mayer, Mary Murphy, Philip Oreopoulos, Sharon Parker, Renante Rondina, Dilip Soman, Christophe Van den Bulte (2025), National Megastudy Shows that Email Nudges to Elementary School Teachers Boost Student Math Achievement, Particularly When Personalized, Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.2418616122

Abstract: In response to the alarming recent decline in US math achievement, we conducted a national megastudy in which 140,461 elementary school teachers who collectively taught 2,992,027 students were randomly assigned to receive a variety of behaviorally informed email nudges aimed at improving students’ progress in math. Specifically, we partnered with the nonprofit educational platform Zearn Math to compare the impact of 15 different interventions with a reminder-only megastudy control condition. All 16 conditions entailed weekly emails delivered to teachers over 4-wk in the fall of 2021. The best-performing intervention, which encouraged teachers to log into Zearn Math for an updated report on how their students were doing that week, produced a 5.06% increase in students’ math progress (3.30% after accounting for the winner’s curse). In exploratory analyses, teachers who received any behaviorally informed email nudge (vs. a reminder-only megastudy control) saw their students’ math progress boosted by an average of 1.89% during the 4-wk intervention period; emails referencing personalized data (i.e., classroom-specific statistics) outperformed emails that did not by 2.26%. While small in size, these intervention effects were consistent across school socioeconomic status and school type (public, private, etc.) and, further, persisted in the 8-wk post-intervention period. Collectively, these findings underscore both how difficult it is to change behavior and the need for large-scale, rigorous, empirical research of the sort undertaken in this megastudy.

Sophia Pink, Jose Cervantez, Erika Kirgios, Edward Chang, Katherine L. Milkman (2025), Can Stereotype Reactance Prompt Women to Compete? A Field Experiment, Organization Science. https://doi.org/10.1287/orsc.2024.19563

Abstract: Women are consistently underrepresented in leadership roles. One contributor may be that women are generally less willing than equally-qualified men to enter competitions (e.g., for jobs or promotions). We draw from research on “stereotype reactance”—the idea that telling people about stereotyped expectations can encourage defiance—to propose and test whether telling women about the gender gap in competition entry can increase their willingness to compete. Our prediction contrasts with prior work on stereotype threat and descriptive norms suggesting that highlighting the gender competition gap might lead women to refrain from competing. In two incentive-compatible, preregistered online experiments, we find that informing women about the gender competition gap increases their likelihood of competing for higher pay, and this effect is mediated by stereotype reactance, consistent with our theorizing. Moreover, exposing both men and women to information about the gender competition gap closes the gap. We then test this informational intervention in a large-scale field experiment on an executive job search platform (n = 4,245), examining whether telling women about the gender competition gap increases their willingness to compete for leadership roles relative to a control message that tells them about an identity-irrelevant competition gap. We find that relative to our control message, informing women about the gender gap in willingness to compete increases submitted job applications by over 20% on the day of condition assignment. This suggests that women’s willingness to compete is affected not just by confidence, but also by cultural expectations and motivation to defy stereotypical norms.

Katie Mehr, Jackie Silverman, Marissa Sharif, Alixandra Barasch, Katherine L. Milkman (2025), The Motivating Power of Streaks: Increasing Productivity Is as Easy as 1, 2, 3, Organizational Behavior and Human Decision Processes. https://doi.org/10.1016/j.obhdp.2025.104391

Abstract: Organizations often use financial incentives to boost employees’ commitment to work-relevant goals in an effort to increase persistence and goal achievement (e.g., to improve organizational efficiency or sales). We introduce and test a novel incentive scheme designed to enhance persistence by increasing commitment to the goal of maximizing earnings. Specifically, we test “streak incentives,” or rewards that offer people increasing payouts for completing multiple consecutive work tasks. Across six pre-registered studies (total N = 4,493), we show that, contrary to standard economic models suggesting people will complete more piece-rate work for larger rewards, people actually complete more work when compensated with streak incentives than with larger, stable incentives. We theorize that this occurs because, by encouraging consecutive task completion, streak incentives increase commitment to a goal of maximizing earnings, which in turn increases persistence. We also show that this effect is not driven by providing increasing rewards; rather, people’s goal commitment and motivation are boosted by the requirement that they complete work tasks consecutively to earn escalating payments. Taken together, our results suggest that designing incentives to encourage streaks of work is a low-cost way to increase goal commitment and therefore persistence in organizations and other contexts.

Rob Kuan, Kristin Blagg, Benjamin Castleman, Rajeev Darolia, Jordan Matsudaira, Katherine L. Milkman, Lesley Turner (2025), Behavioral Nudges Prevent Loan Delinquencies At Scale: A 12-Million Person Field Experiment, Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.2416708122

Abstract: Americans collectively hold over $1.6 trillion in student loan debt, and over the last decade millions of borrowers have defaulted on loans, with serious consequences for their financial health. In a 13-million-person field experiment with the U.S. Department of Education, we tested the effectiveness of different email interventions to inform borrowers about alternative repayment options after a missed loan payment. Our interventions tested whether sending monthly behaviorally-informed emails, providing follow-up reminders, framing benefits in percentage (vs. dollar) terms, and providing just one recommended action step at a time (vs. two) affected borrower outcomes. We find that i) behaviorally-informed emails reduce estimated 60-d delinquencies by 0.42 pp, ii) reminders boost the efficacy of such emails by 0.57 pp, iii) describing potential savings in percentage terms is more effective than describing these benefits in dollar terms, reducing estimated delinquencies by 0.14 pp, and iv) encouraging two actions (i.e., enrollment in income-driven repayment plans and auto debit programs) repeatedly across two emails is marginally more effective than encouraging one action at-a-time across two emails, reducing estimated delinquencies by 0.05 pp. Overall, if scaled to all 13-million borrowers in our experiment, we estimate that our best-performing intervention would have averted approximately 79,800 60-d delinquencies. Our findings i) highlight the benefits of describing potential savings in percentage terms, which may magnify perceived savings for recipients, ii) underscore the risks of oversimplification, and iii) demonstrate that nudges can be an effective, low-cost complement to other policies for reducing delinquencies and supporting borrowers with student loan debt.

Jose A. Cervantez and Katherine L. Milkman (2024), Can Nudges Be Leveraged to Enhance Diversity in Organizations? A Systematic Review, Current Opinion in Psychology. https://doi.org/10.1016/j.copsyc.2024.101874

Abstract: In this article, we review and summarize key findings from a growing literature exploring how nudges can facilitate efforts to diversify organizations. Nudges are psychologically-informed interventions that change behavior without restricting choice or altering incentives. We focus on two types of nudges to enhance organizational diversity: (1) nudges that target organizational processes directly or the decision makers who oversee them to increase the diversity of those hired and promoted and (2) nudges that target the underrepresented candidates themselves to increase the diversity of those applying for organizational roles. We categorize nudges designed to enhance organizational diversity, both by their target and based on the psychology they leverage to improve outcomes for women and racial minorities.

Linda W. Chang, Erika Kirgios, Sendhil Mullainathan, Katherine L. Milkman (2024), Does Counting Change What Counts? Quantification Fixation Biases Decision Making, Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.2400215121

Abstract: People often rely on numeric metrics to make decisions and form judgments. Numbers can be difficult to process, leading to their underutilization, but they are also uniquely suited to making comparisons. Do people decide differently when some dimensions of a choice are quantified and others are not? We explore this question across 21 preregistered experiments (8 in the main text, N = 9,303; 13 in supplement, N = 13,936) involving managerial, policy, and consumer decisions. Participants face choices that involve tradeoffs (e.g., choosing between employees, one of whom has a higher likelihood of advancement but lower likelihood of retention), and we randomize which dimension of each tradeoff is presented numerically and which is presented qualitatively (using verbal estimates, discrete visualizations, or continuous visualizations). We show that people systematically shift their preferences toward options that dominate on tradeoff dimensions conveyed numerically—a pattern we dub “quantification fixation.” Further, we show that quantification fixation has financial consequences—it emerges in incentive-compatible hiring tasks and in charitable donation decisions. We identify one key mechanism that underlies quantification fixation and moderates its strength: When making comparative judgments, which are essential to tradeoff decisions, numeric information is more fluent than non-numeric information. Our findings suggest that when we count, we change what counts.

Katherine L. Milkman, Sean F. Ellis, Dena Gromet, Alex S. Luscher, Rayyan S. Mobarak, Madeline K. Paxson, Ramon A. Silvera Zumaran, Robert Kuan, Ron Berman, Neil A. Lewis Jr. John A. List, Mitesh S. Patel, Christophe Van den Bulte, Kevin G. Volpp, Maryann V. Beauvais, Jonathan K. Bellows, Cheryl A. Marandola, Angela Duckworth (2024), Megastudy Shows That Reminders Boost Vaccination But Adding Free Rides Does Not, Nature. https://doi.org/10.1038/s41586-024-07591-x

Abstract: Encouraging routine COVID-19 vaccinations is likely to be a crucial policy challenge for decades to come. To avert hundreds of thousands of unnecessary hospitalizations and deaths, adoption will need to be higher than it was in the autumn of 2022 or 2023, when less than one-fifth of Americans received booster vaccines. One approach to encouraging vaccination is to eliminate the friction of transportation hurdles. Previous research has shown that friction can hinder follow-through and that individuals who live farther from COVID-19 vaccination sites are less likely to get vaccinated. However, the value of providing free round-trip transportation to vaccination sites is unknown. Here we show that offering people free round-trip Lyft rides to pharmacies has no benefit over and above sending them behaviourally informed text messages reminding them to get vaccinated. We determined this by running a megastudy with millions of CVS Pharmacy patients in the United States testing the effects of (1) free round-trip Lyft rides to CVS Pharmacies for vaccination appointments and (2) seven different sets of behaviourally informed vaccine reminder messages. Our results suggest that offering previously vaccinated individuals free rides to vaccination sites is not a good investment in the United States, contrary to the high expectations of both expert and lay forecasters. Instead, people in the United States should be sent behaviourally informed COVID-19 vaccination reminders, which increased the 30-day COVID-19 booster uptake by 21% (1.05 percentage points) and spilled over to increase 30-day influenza vaccinations by 8% (0.34 percentage points) in our megastudy. More rigorous testing of interventions to promote vaccination is needed to ensure that evidence-based solutions are deployed widely and that ineffective but intuitively appealing tools are discontinued.

Aneesh Rai, Edward Chang, Erika Kirgios, Katherine L. Milkman (2024), Group Size and Its Impact on Diversity-Related Perceptions and Hiring Decisions in Homogeneous Groups, Organizational Science. https://doi.org/10.1287/orsc.2020.14705

Abstract: Why do some homogeneous groups face backlash for lacking diversity, whereas others escape censure? We show that a homogeneous group’s size changes how it is perceived and whether decision makers pursue greater diversity in its ranks. We theorize that people make different inferences about larger groups than smaller ones—with consequences for diversity management—due to Bayesian reasoning. This can produce sensitivity to a lack of diversity in large groups and limited sensitivity to a lack of diversity in small groups. Because each group member represents the outcome of a hiring decision, larger homogeneous groups signal a diversity problem more strongly than smaller homogeneous groups. Across three preregistered experiments (n = 4,283), we show that decision makers are more likely to diversify larger homogeneous groups than smaller ones and view larger homogeneous groups as (i) more likely to have resulted from an unfair selection process; (ii) less diverse; (iii) more likely to face diversity-related impression management concerns; and (iv) less open to the influence of newly added underrepresented members. Further, (i)–(iii) mediate the relationship between homogeneous group size and decisions to diversify. We extend our findings to S&P 1500 corporate boards, showing that larger homogeneous boards are more likely to add women or racial minorities as directors. Larger homogeneous boards are also rarer than expected, whereas smaller homogeneous boards are surprisingly abundant. This suggests that decision makers neglect homogeneity in smaller groups, while investing extra effort toward diversifying larger homogeneous groups. Our findings highlight how group size shapes diversity-related perceptions and decisions and identify mechanisms that kickstart diversification efforts.

Rachel Gershon, Cynthia Cryder, Katherine L. Milkman (2024), Friends with Health Benefits: A Field Experiment, Management Science. https://doi.org/10.1287/mnsc.2022.01401

Abstract: When pursuing goals, we commonly choose between going it alone versus teaming up together. In a field experiment (n = 774), we tested the benefits of rewarding individual versus tandem goal pursuit. In a standard-reward condition, we experimentally offered gym members an individual cash reward each day they visited the gym for four weeks. Participants in a tandem-reward condition could earn the same reward but only if they surmounted an extra logistical hurdle: they had to visit the gym with a friend. Although this additional requirement made it more difficult for participants in the tandem-reward condition to earn equivalent incentives, participants with this extra hurdle visited the gym about 35% more frequently than those earning a standard reward. A follow-up survey suggests that tandem rewards provide nonmonetary incentives that change behavior, including increased accountability and enjoyment. Our findings illustrate the advantages of making desired behaviors social to promote follow-through.

Kai Ruggeri, Friederike Stock, S. Alexander Haslam, Valerio Capraro, Paulo Boggio, Naomi Ellemers, Aleksandra Cichoka, Karen M. Douglas, David Rand, Sander van der Linden, Mina Cikara, Eli J. Finkel, James N. Druckman, Michael J.A. Wohl, Richard E. Petty, Joshua A. Tucker, Azim Shariff, Michele Gelfand, Dominic Packer, Jolanda Jetten, Paul A.M. Van Lange, Gordon Pennycook, Ellen Peters, Katherine Biacker, Alia Crum, Kim A. Weeden, Lucy Napper, Nassim Tabri, Jamil Zaki, Linda Skitka, Shinobu Kitayama, Dean Mobbs, Cass R. Sunstein, Sarah Ashcroft-Jones, Anna L. Todsen, Ali Hajian, Sanne Verra, Vanessa Buehler, Maja Friedemann, Marlene Hecht, Rayyan S. Mobarak, Ralitsa Karakasheva, Markus R. Tunte, Siu Kit Yeung, R. Shayna Rosenbaum, Zan Lep, Yuki Yamada, Sa-kiera T.J. Hudson, Lucia Macchia, Irina Soboleva, Eugen Dimant, Sandra J. Geiger, Hannes Jarke, Tobias Wingen, Jana B. Berkessel, Silvana Mareva, Lucy McGill, Francesca Papa, Bojana Veckalov, Zeina Afif, Eike K. Buabang, Marna Landman, Felice Tavera, Jack L. Andrews, Asli Burgalioglu, Zorana Zupan, Lisa Wagner, Joaquin Navajas, Marek Vranka, David Kasdan, Patricia Chen, Kathleen R. Hudson, Lindsay M. Novak, Paul Teas, Nikolay R. Rachev, Matteo M. Galizzi, Marija Petrovic, Katherine L. Milkman, Jay J. Van Bavel, Robb Willer (2023), A Synthesis of Evidence for Policy From Behavioural Science During COVID-19, Nature. https://doi.org/10.1038/s41586-023-06840-9

Abstract: Scientific evidence regularly guides policy decisions, with behavioural science increasingly part of this process. In April 2020, an influential paper proposed 19 policy recommendations (‘claims’) detailing how evidence from behavioural science could contribute to efforts to reduce impacts and end the COVID-19 pandemic. Here we assess 747 pandemic-related research articles that empirically investigated those claims. We report the scale of evidence and whether evidence supports them to indicate applicability for policymaking. Two independent teams, involving 72 reviewers, found evidence for 18 of 19 claims, with both teams finding evidence supporting 16 (89%) of those 18 claims. The strongest evidence supported claims that anticipated culture, polarization and misinformation would be associated with policy effectiveness. Claims suggesting trusted leaders and positive social norms increased adherence to behavioural interventions also had strong empirical support, as did appealing to social consensus or bipartisan agreement. Targeted language in messaging yielded mixed effects and there were no effects for highlighting individual benefits or protecting others. No available evidence existed to assess any distinct differences in effects between using the terms ‘physical distancing’ and ‘social distancing’. Analysis of 463 papers containing data showed generally large samples; 418 involved human participants with a mean of 16,848 (median of 1,699). That statistical power underscored improved suitability of behavioural science research for informing policy decisions. Furthermore, by implementing a standardized approach to evidence selection and synthesis, we amplify broader implications for advancing scientific evidence in policy formulation and prioritization.