Research

Can Nudges Increase COVID-19 Vaccine Completion in Kenya? (with Florence Aketch, Elisa M. Maffioli, James Otieno, Leah R. Rosenzweig, and Wendy N. Wong)

Journal of Development Economics, 2025

Policymakers aiming at inducing behavior change often rely on nudges: interventions designed to influence people’s decisions without restricting their choices. Partnering with the Ministry of Health in Kenya, we tested a series of nudges to encourage COVID-19 vaccination completion among people overdue for their second dose of a two-dose primary series. Based on principles from behavioral science, we conducted four experiments between July 2022 and January 2023, randomly providing 51,903 individuals with Short-Message-Services (SMS) messages and financial incentives to return for a second dose. We find no evidence that any of the nudges significantly increased vaccination completion rates. Phone survey follow-ups among a subsample reveal that 91.4% of people recalled receiving the message, but 83.7% of the sample was not worried or only a little worried about COVID-19. Two to three years into a pandemic, nudges like SMSs and financial incentives may not generate meaningful behavior change.

The Endowment Effect and Collateralized Loans (with Michael Kremer, Xinyue Lin, and Gautam Rao)

Revise and Resubmit, Econometrica

Collateral requirements play an important role in credit markets. This paper shows that the endowment effect—the phenomenon where owing a good increases one's valuation of it—inhibits demand for loans which use a borrower's existing assets as collateral. Using a field experiment in Kenya, we show that borrowers instead strongly prefer loans collateralized using the new durable assets being financed by the loans themselves. They are willing to pay 9% per month higher interest for such Same-Asset Collateralized Loans (SACLs) despite the endowed and new assets being randomized, and thus similarly valued before ownership. Our findings imply that assets which are difficult to use as collateral—which cannot be financed by SACLs—will be invested in less, even if the borrower has other collateral. We argue that borrowers' preference for SACLs is driven by naivete: they initially perceive that they have little to lose when offered a SACL, but subsequently come to develop an attachment to the new asset, resulting in high repayment effort. Consistent with this, borrowers underestimate their future attachment to an asset before owning it, and SACLs do not have higher default rates despite having higher demand. We derive the conditions under which offering consumers SACLs increases or conversely decreases borrower welfare.

Outreach Without Overreach:  A Vaccination Campaign in Kenya Does Not Create Backlash (with Michael Kremer, Elisa Maffioli, Leah Rosenzweig, and Wendy Wong)

Revise and Resubmit, Review of Economics and Statistics

Following the COVID-19 pandemic, concerns have emerged that certain policy interventions perceived as intrusive—such as offering vaccination at individuals’ homes—may erode public trust in government. One view emphasizes making vaccination convenient to overcome logistical barriers. Another warns that such strategies risk creating pressure, provoking resistance, and undermining long-term confidence in government authorities. We explore this tension in the context of a COVID-19 vaccination program in Kenya, where government health workers conducted household visits encouraging adults to get vaccinated at nearby sites. Our findings from a randomized field experiment show no evidence of backlash. First, increases in vaccination rates were sustained over time. Second, drawing on previous economics research on social pressure, we examined whether individuals are more responsive when given advance notice of a visit and an offer of vaccination, or whether such notice leads them to avoid the encounter. Contrary to concerns about pressure from governmental health workers, we find that advance notice increases vaccine uptake. These findings suggest that outreach by governmental health workers can improve vaccine coverage without undermining public trust, highlighting the importance of access and convenience in policy interventions. 

Financial Incentives, Health Screening, and Selection into Mental Health Care: Experimental Evidence from College Students in India (with Emily Breza, Vijaya Raghavan, Kailash Rajah, Thara Rangaswamy, Gautam Rao, Frank Schilbach, Sobia Shadbar, and James Stratton)

Revise and Resubmit, Journal of the European Economics Association

In an RCT with college students in Chennai (N=340), we test how modest financial incentives and personalized feedback affect the uptake and targeting (by symptom severity) of free therapy. Despite 56% of students screening positive for at least mild depression or anxiety, only 3% in the control group took up therapy. A small cash incentive increased appointments by 9 percentage points (p = 0.06) on average without substantially affecting targeting. Personalized feedback and recommendations based on a mental health screening tool significantly improved targeting while keeping overall take-up largely unchanged. Combining these two treatments achieved both higher take-up and improved targeting, by increasing appointments among symptomatic individuals by 21 pp (p < 0.01) without affecting uptake by asymptomatic individuals. These findings suggest that low-cost incentives coupled with screening information can effectively increase uptake while allocating limited mental health care resources to those with greater need.

Campaigns and Conversations: Experimental Evidence on the Political Effects of WhatsApp 

Messaging applications have become central to how people communicate and, increasingly, to how political campaigns reach voters. Unlike traditional media, these platforms combine vertical communication from political actors with horizontal communication among individuals. Using an experiment on WhatsApp during a large Indian election, I randomized participants to join chat groups organized by political parties or to a control. To understand the role of horizontal communication between users, a second treatment arm exposed participants to the posts of party officials but not to posts by other group members. Full groups shifted political preferences toward the organizing party and changed perceptions of other voters' preferences, increasing perceived support for the eventual winner. The party-content-only treatment generated no such effects. Administrative data show greater attention but faster exit in full groups. These results demonstrate how messaging applications are more than just a broadcast tool: horizontal communication between individuals is key to their effects.

Guarantor Networks, Financial Contagion, and Systemic Risk: Evidence from Kenya (with Paul Brimble and Josh Deutschmann)

Social ties underpin much of formal and informal finance in low- and middle-income countries. One concern about the use of social ties to secure loans is the potential for coordinated or strategic behavior to cause defaults to cascade. In this paper, we provide a novel characterization of the network defined by loan guarantees in a financial cooperative in Kenya. The network is highly interconnected, with most members forming a single large connected component. We then study how production shocks propagate through this network. We find that production shocks increase the likelihood of loan nonperformance both directly, for the shocked borrower, and indirectly, for borrowers connected to them through guarantee ties. Because the network is densely connected, these indirect effects aggregate to a sizeable share of the total short-term repayment impact of a shock. We complement these causal estimates with a model of financial contagion that distinguishes correlated shocks from network cascades, and use it to quantify the SACCO's exposure to systemic risk. These findings highlight a trade-off between expanding credit access through social collateral and containing systemic risk.

Teaching Mental Health: Evaluating India's Happiness Curriculum (with Avinash Moorthy)

Data collection complete

Better Borrowing to Promote Access to Water and Improve Dairy Farming in Kenya (with Suleiman Asman, Joshua Deutschmann, Michael Kremer, and Gautam Rao)

Data collection in progress