Jeremy Magruder

Learning from the Crowd: Regression Discontinuity Estimates of the Effects of an Online Review Database

Internet review forums increasingly supplement expert opinion and social networks in informing consumers about product quality. However, limited empirical evidence links digital word‐of‐mouth to purchasing decisions. We implement a regression discontinuity design to estimate the effect of positive Yelp.com ratings on restaurant reservation availability. An extra half‐star rating causes restaurants to sell out 19 percentage points (49%) more frequently, with larger impacts when alternate information is more scarce. These returns suggest that restaurateurs face incentives to leave fake reviews but a rich set of robustness checks confirm that restaurants do not manipulate ratings in a confounding, discontinuous manner.

Marital Shopping and Epidemic AIDS

HIV risks decline sharply at age 30 for women in South Africa, long before coital frequencies or pregnancies decrease. I evaluate several prominent behavioral models of HIV, and find that these do not suggest sharply decreasing risks with age. I formulate a model of spousal search and find that “marital shopping” can generate epidemic HIV prevalence despite low transmission rates because search behavior interacts with dynamics of HIV infectiousness. The implied age-infection profile closely mimics that in South Africa, and the suggested behavior matches that reported by South Africans. Condom use in new relationships and transmission rate reductions are both found to be effective policies and, when used together, eliminate the potential of spousal search to spread HIV. In contrast, antiretroviral treatment is found to have only a minimal effect on the epidemic.

Do Job Networks Disadvantage Women? Evidence from a Recruitment Experiment in Malawi

We use a field experiment to show that referral-based hiring has the potential to disadvantage qualified women, highlighting another potential channel behind gender disparities in the labor market. Through a recruitment drive for a firm in Malawi, we look at men’s and women’s referral choices under different incentives and constraints. We find that men systematically refer few women, despite being able to refer qualified women when explicitly asked for female candidates. Performance pay also did not alter men’s tendencies to refer men. In addition, women did not refer enough high-quality women to offset men’s behavior.

Can Network Theory-based Targeting Increase Technology Adoption?

In order to induce farmers to adopt a productive new agricultural technology, we apply simple and complex contagion diffusion models on rich social network data from 200 villages in Malawi to identify seed farmers to target and train on the new technology. A randomized controlled trial compares these theory-driven network targeting approaches to simpler strategies that either rely on a government extension worker or an easily measurable proxy for the social network (geographic distance between households) to identify seed farmers. Our results indicate that technology diffusion is characterized by a complex contagion learning environment in which most farmers need to learn from multiple people before they adopt themselves. Network theory based targeting can out-perform traditional approaches to extension, and we identify methods to realize these gains at low cost to policymakers. Keywords: Social Learning, Agricultural Technology Adoption, Complex Contagion, Malawi JEL Classification Codes: O16, O13

Labour Market Responses To Immigration: Evidence From Internal Migration Driven By Weather Shocks

We study the labour market impact of internal migration in Indonesia by instrumenting migrant flows with rainfall shocks at the origin area. Estimates reveal that a one percentage point increase in the share of migrants decreases income by 0.97% and reduces employment by 0.24 percentage points. These effects are different across sectors: employment reductions are concentrated in the formal sector, while income reduction occurs in the informal sector. Negative consequences are most pronounced for low‐skilled natives, even though migrants are systematically highly skilled. We suggest that the two‐sector nature of the labour market may explain this pattern.