Publications











Working Papers


"Digital Advertising and Market Structure: Implications for Privacy Regulation" [with Daniel Deisenroth, Utsav Manjeer, Zarak Sohail, and Steve Tadelis] (2026)


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” [with Steve Tadelis, Christopher Hooton, Utsav Manjeer, Daniel Deisenroth, 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.