Publications

Brynjolfsson E,  Collis A, Deisenroth D, Garro H, Kutzman D, Liaqat A, & Wernerfelt N (2025). "The Consumer Welfare Effects of Online Ads: Evidence from a 9-Year Experiment." American Economic Review: Insights

Wernerfelt N*, Tuchman A, Shapiro B, & Moakler R. (2024). "Estimating the Value of Offsite Tracking Data to Advertisers: Evidence from Meta." Marketing Science. [Job Market Paper; Finalist, John D. C. Little Award]

Alekseev G, Amer S, Gopal M, Kuchler T, Schneider JW, Stroebel J, & Wernerfelt N (2023). “The Effects of COVID-19 on US Small Businesses: Evidence from Owners, Managers, and Employees.” Management Science.

Athey S, Grabarz K, Luca M, & Wernerfelt N. (2023). “Digital Public Health Interventions at Scale: The Impact of Social Media Advertising on Beliefs and Outcomes Related to COVID Vaccines.” Proceedings of the National Academy of Sciences.

Chetty R*, Jackson MO*, Stroebel J*, Kuchler T*, Hendren N*, Fluegge R, Gong S, Gonzalez F, Grondin A, Jacob M, Johnston D, Koenen M, Laguna-Muggenburg E, Mudekereza F, Rutter T, Thor N, Townsend W, Zhang R, Bailey M, Barbera P, Bhole M, & Wernerfelt N. (2022). “Social Capital in the United States II: Exposure, Friending Bias, and the Determinants of Economic Connectedness.” Nature.

Chetty R*, Jackson MO*, Stroebel *J, Kuchler T*, Hendren N*, Fluegge R, Gong S, Gonzalez F, Grondin A, Jacob M, Johnston D, Koenen M, Laguna-Muggenburg E, Mudekereza F, Rutter T, Thor N, Townsend W, Zhang R, Bailey M, Barbera P, Bhole M, & Wernerfelt N. (2022). “Social Capital in the United States I: Measurement and Associations with Economic Mobility.” Nature.

Working Papers

“The Digital Welfare of Nations: New Measures of Welfare Gains and Inequality” [Erik Brynjolfsson*, Avinash Collis*, Asad Liaqat, Daley Kutzman, Haritz Garro, Daniel Deisenroth, and Nils Wernerfelt] NBER Digest (2023) accepted in principle, Nature Human Behaviour

Abstract: Digital goods can generate large benefits for consumers, but these benefits are largely unmeasured in the national accounts, including GDP and productivity. In this paper, we measure welfare gains from 10 popular digital goods across 13 countries by conducting large-scale incentivized online choice experiments on representative samples of nearly 40,000 people. We estimate that these goods – many of which are free to users – generate over $2.5 trillion in aggregate consumer welfare across these countries per year, which is roughly equivalent to 6% of their combined GDP. We find that lower-income individuals and lower-income countries obtain relatively larger welfare gains from these goods compared to higher-income individuals and countries. This suggests that digital goods may reduce inequality in welfare within and across countries by disproportionately benefiting lower-income groups.

"Reducing misinformation sharing at scale using digital accuracy prompt ads" [Hause Lin*, Haritz Garro*, Nils Wernerfelt*, Jesse Shore, Adam Hughes, Daniel Deisenroth, Nathaniel Barr, Adam Berinsky, Dean Eckles, Gordon Pennycook, and David G. Rand] (2024)  accepted in principle, Nature Human Behaviour

Abstract: Interventions to reduce misinformation sharing have been a major focus in recent years. Developing “content-neutral” interventions that do not require specific fact-checks or warnings related to individual false claims is particularly important in developing scalable solutions. Here, we provide the first evaluations of a content-neutral intervention to reduce misinformation sharing conducted at scale in the field. Specifically, across two on-platform randomized controlled trials, one on Meta’s Facebook (N=33,043,471) and the other on Twitter (N=75,763), we find that simple messages reminding people to think about accuracy—delivered to large numbers of users using digital advertisements—reduce misinformation sharing, with effect sizes on par with what is typically observed in digital advertising experiments. On Facebook, in the hour after receiving an accuracy prompt ad, we found a 2.6% reduction in the probability of being a misinformation sharer among users who had shared misinformation the week prior to the experiment. On Twitter, over more than a week of receiving 3 accuracy prompt ads per day, we similarly found a 3.7% to 6.3% decrease in the probability of sharing low-quality content among active users who shared misinformation pre-treatment. These findings suggest that content-neutral interventions that prompt users to consider accuracy have the potential to complement existing content-specific interventions in reducing the spread of misinformation online. 

"Digital Advertising and Market Structure: Implications for Privacy Regulation" [Daniel Deisenroth, Utsav Manjeer, Zarak Sohail, Steven Tadelis, and Nils Wernerfelt] (2024)

Abstract: We study how changes in the effectiveness of targeted digital advertising shape firm behavior and product-market outcomes. We leverage the introduction of Apple's App Tracking Transparency (ATT) framework, which limited online advertisers' access to user data and thus substantially reduced their advertising effectiveness. Using proprietary advertiser-level data from Meta and industry-level outcomes from the Bureau of Labor Statistics, we show that greater exposure to the ATT shock led to lower ad spend, fewer establishments, and higher product prices. The findings suggest that digital advertising primarily expands markets and that privacy policies can have unintended consequences on product market competition.

“Learning, Sophistication, and the Returns to Advertising: Implications for Differences in Firm Performance” [Steven Tadelis*, Christopher Hooton, Utsav Manjeer, Daniel Deisenroth, Nils Wernerfelt, Nick Dadson and Lindsay Greenbaum.]  (2023)

Abstract: Why do establishments exhibit wide variation in their productivity and profitability? Can variation in returns to advertising help answer this question? We present results from a large field experiment on Facebook and Instagram that documents variance in advertisers’ ability to generate returns to advertising. We focus on campaigns aimed at boosting sales and tie advertising expenses to revenues for each advertiser. We find that spending on advertising led to significant increases in revenues, number of purchases, number of purchasers, and number of conversions. The heterogeneity in these results by expenditure, age, and engagement documents patterns consistent with learning by doing and variance in how sophisticated advertisers are. Advertisers who engage in more learning activities and more sophisticated data collection exhibit the highest returns and are more likely to continue their activities over time, suggesting that differences in advertising effectiveness may account for some of the variance in productivity across firms.

Casework

Ascarza, Eva, Alex Schultz, and Nils Wernerfelt. "Growing with Digital Marketing: Evidence, Metrics, and Mistakes." Harvard Business School Case 526-040, March 2026. View Details

Earlier Publications

Wernerfelt N, Slusky DJG, & Zeckhauser R. (2017). “Second Trimester Sunlight and Asthma: Evidence from Two Independent Studies.” American Journal of Health Economics. 3(2): 227-253.

Dreber A, Rand DG, Wernerfelt N, Garcia JR, Lum JK, & Zeckhauser R. (2011). “Dopamine and Risk Choices in Different Domains: Findings Among Serious Tournament Bridge Players.” Journal of Risk and Uncertainty. 43: 19-38.

Rand DG, Pfeiffer T, Dreber A, Sheketoff R, Wernerfelt N, & Benkler Y. (2009). “Dynamic Remodeling of In-group Bias During the 2008 Presidential Election.” Proceedings of the National Academy of Sciences. 106 (15): 6187-6191.

Other Publications

Doudchenko N, Gilinson D, Taylor S, & Wernerfelt N. (2019). “Designing Experiments with Synthetic Controls.”  Working paper (resting).

Amsden Z, et al. (2019). “The Libra Blockchain.” Technical White Paper.

Wernerfelt N, & Zeckhauser R. (2010). “Denying the Temptation to GRAB.” Chapter in The Natural Resources Trap. Ed. W Hogan and F Sturzenegger. Cambridge, MA: MIT Press.

Wernerfelt N, Tarnita C, Rand DG, & Nowak M. (2009) “A Modular Approach for Analyzing Evolutionary Games in Networked Populations.” Harvard College Mathematics Thesis.