Associate Professor of Behavioral Science
Punctuated Decline of Human Cooperation.
Sabin, Nicholas, Klinowski, David, & Felix Reed-Tsochas. (2026).
Nature.
https://doi.org/10.1038/s41586-026-10380-3. Publisher.
Human cooperation is dynamic and often declines even under favourable conditions. Many prevailing theories explain the decrease of cooperation in terms of strategic behaviour or learning, framed as evidence of rational behaviour or progression towards rationality. Here we show that a key source of long-term decline derives from deviations from rational behaviour that systematically vary over time. We analyse a natural social dilemma in the field—that is, group lending in Sierra Leone—tracking cooperative dynamics over a five-year period. Borrowers enter a joint-liability contract, structured so that if the group loan is not repaid in full, all members lose access to future credit. This produces a threshold social dilemma with incentives to free-ride. The dataset includes 47,931 group payments made by 7,108 borrowers, augmented with a two-stage cluster sample of semi-structured interviews. We find a statistically robust pattern of punctuated decline driven by behavioural mechanisms. Cooperation rates start out high but gradually decline due to decreases in group members’ cooperative motivation and effort. Sharp rebounds occur when loans are restarted and clients resensitized to their cooperative responsibilities, even though the group membership and dilemma structure are largely unchanged. This pattern persists over the five-year observation window, but with each successive restart the subsequent decline is more rapid. The findings have direct implications for preventing behavioural decline in cooperative programmes and institutions.
Replication Package for Punctuated Decline of Human Cooperation.
Sabin, Nicholas, Klinowski, David, & Felix Reed-Tsochas. (2026).
Open Science Framework.
https://doi.org/10.17605/OSF.IO/26BFC. OSF.
The replication package for “Punctuated Decline of Human Cooperation” (Sabin, Klinowski, & Reed-Tsochas, 2026) is publicly available at the Open Science Framework. The package includes the deidentified group lending data and Stata code to reproduce the statistical analysis and figure source data.
Unlocking Innovation: The Dynamics of User Engagement in an Open-Source 3D Printer Community.
Garmulewicz, Alysia, Sabin, Nicholas, & Felix Reed-Tsochas. (2025).
PLoS ONE. 20(4): e0321963.
https://doi.org/10.1371/journal.pone.0321963. Publisher. PDF.
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User innovation lies at the core of a growing body of research, with a predominant focus on how individual user attributes can be associated with observed contributions to innovation. However, framing user innovation in terms of individual attributes risks neglecting important changes in behavior at the individual and community level over time. Here, our focus is on how the time that individual users spend in that community relates to innovation outcomes. We study innovation in a firm-hosted online user community for a 3D printer company, marked by their commitment to open-source hardware. We analyze a unique longitudinal dataset of 38,277 observations recording user posts to an open-access user forum from October 2011 to March 2015. We find that time spent in a user community is positively associated with contributions to innovation, as users migrate from identifying problems and needs, to contributing innovation-related modifications and hacks. Our finding emphasizes the value of user retention in open-source communities as our analysis shows that typical users can add value to firms’ innovation activities over time. Our focus on open-hardware complements many existing studies on open-source software and advances our understanding of open innovation more generally.
Choosing Partners: Selection Priorities of Joint Liability Group Leaders.
Sabin, Nicholas. (2023).
Empirical Economics. 64: 323–348.
https://doi.org/10.1007/s00181-022-02249-x. Publisher. PDF.
Joint liability credit groups are often formed through a self-selection process. Partner choice presents complex tradeoffs between behavioral expectations, risk diversification, monitoring, and enforcement. Most prior studies have found partner selection to be non-optimal financially. In this study, we explore social, spatial, economic, and demographic factors that may be driving the selection process. A unique analytical approach is used based on the selection order of partners in joint liability groups. We decompose a group leader’s sequence of partner invitations into a series of ranked choices. The results indicate that socially and spatially proximate members are likely to be prioritized in the selection process, even though other potential members may possess stronger financial traits, such as higher monthly sales or business equity. There is also evidence of early selection based on gender, marital status, children, and matching business type. The analysis suggests that partner selection may be driven by social incentives and the avoidance of strategic default. More broadly, this study suggests which factors are prioritized when actors have choice over whom to partner with in a social dilemma.
Moral Dilemmas and Trust in Leaders During a Global Health Crisis.
Everett, J.A.C., Colombatto, C., Awad, E., Boggio, P., Bos, B., Brady, W.J., Chawla, M., Chituc, V., Chung, D., Drupp, M.A., Goel, S., Grosskopf, B., Hjorth, F., Ji, A., Kealoha, C., Kim, J.S., Lin, Y., Ma, Y., Maréchal, M.A., Mancinelli, F., Mathys, C., Olsen, A.L., Pearce, G., Prosser, A.M.B., Reggev, N., Sabin, N., Senn, J., Sinnott-Armstrong, W., Shin, Y.S., Sjastad, H., Strick, M., Sul, S., Tummers, L., Turner, M., Yu, H., Zoh, Y., & Crockett, M.J. (2021).
Nature Human Behaviour. 5: 1074–1088.
https://doi.org/10.1038/s41562-021-01156-y.
Publisher. PDF. Registration. Data & Code.
Trust in leaders is central to citizen compliance with public policies. One potential determinant of trust is how leaders resolve conflicts between utilitarian and non-utilitarian ethical principles in moral dilemmas. Past research suggests that utilitarian responses to dilemmas can both erode and enhance trust in leaders: sacrificing some people to save many others (‘instrumental harm’) reduces trust, while maximizing the welfare of everyone equally (‘impartial beneficence’) may increase trust. In a multi-site experiment spanning 22 countries on six continents, participants (N = 23,929) completed self-report (N = 17,591) and behavioural (N = 12,638) measures of trust in leaders who endorsed utilitarian or non-utilitarian principles in dilemmas concerning the COVID-19 pandemic. Across both the self-report and behavioural measures, endorsement of instrumental harm decreased trust, while endorsement of impartial beneficence increased trust. These results show how support for different ethical principles can impact trust in leaders, and inform effective public communication during times of global crisis.
Able but Unwilling to Enforce: Cooperative Dilemmas in Group Lending.
Sabin, Nicholas, & Felix Reed-Tsochas. (2020).
American Journal of Sociology. 125 (6): 1602-1667. https://doi.org/10.1086/709105. Publisher. PDF.
It is known that greater social cohesion increases a group’s ability to enforce cooperation. Despite this, defectors often go unpunished, and groups with social structures that are a priori favorable often fail. A critical distinction is required between the structural effect on ability versus willingness to punish. The authors develop a theoretical framework in which variation in a group’s social structure generates a tension between ability and willingness to enforce cooperation. Structures that promote ability to punish also often reduce interest in carrying out sanctions, thus changing collective outcomes. The authors’ empirical analysis involves a well-defined cooperative dilemma: group lending in Sierra Leone. They complement statistical modeling, based on a data set containing 5,487 group repayments,with ethnographic analysis. They find that (1) structural cohesion only increases economic cooperation between borrowers to a point, beyond which unwillingness outweighs increased ability to punish, reducing group repayments, and that (2) groups with disconnected subgroups perform worse on average. Although borrowers are more willing to punish defectors in the out-subgroup, they are unable to do so effectively.
The Cognitive Effects of Economic Scarcity on Decision Making in Chile.
Principal Investigator: Sabin, Nicholas. (2020-2023).
Research Grant awarded by the National Agency for Research and Development (ANID).
Fondecyt de Iniciación en Investigación. ($83,000,000 CLP). Funder.
Research has identified a 'scarcity mindset' as systematically affecting economic decision-making. This mindset occurs when people feel resources are low relative to needs. A scarcity mindset may occur chronically, for example when a single parent consistently does not have enough money to pay the bills, or it may occur acutely in a specific circumstance, for example in the current crisis of COVID-19 many citizens worry about access to basic food and supplies. To date, the scarcity mindset has been linked to economic decision making in terms of increased risk aversion, increased temporal discounting, and decreased cognitive function. We intend to explore how a scarcity mindset affects a different aspect of decision making: prosocial behavior. This topic is of significant interest given the central role of social interaction and cooperation in a well-functioning society. The COVID-19 pandemic highlights the importance of accurately modelling social behavior in a crisis situation. If we can better understand when economic scarcity may trigger irrational decisions, we would be more able to help ourselves and others make deliberate decisions for the public good.
Microfinance: A Field in Flux.
Sabin, Nicholas. (2015).
Social Finance. Editors: Nicholls, Alex, Paton, Rob, & Jed Emerson.
(First Edition, 156-184). Oxford: Oxford University Press. https://doi.org/10.1093/acprof:oso/9780198703761.003.0007 Publisher. PDF.
Financial access for poor and low-income clients has expanded dramatically over the last four decades. This chapter provides an overview of the microfinance landscape and highlights key debates within the field. The market structure is shifting, with organizations increasingly accessing commercial funding. Some geographic markets have overheated, producing substantial criticism. Recent impact evaluations are raising questions about what microfinance actually can and should attempt to achieve. Even the basic offering is being rethought in terms of products and services that may better suit the needs of the poor. This changing landscape is placed in its historical context, noting key predecessors and how the microfinance movement began and grew to its present form. Contrasting perspectives are structured around three ongoing debates: the critical features of modern microfinance, the appropriate role of commercialization, and the assessment of microfinance’s impact. The chapter concludes with implications for the broader field of social finance.