Working papers :
M. Lambotte and B. Montmartin, Conformity, Competition, and Voluntary Price Regulation: Evidence from French Physicians. New version (November 2025) - R&R at the Journal of the European Economic Association
This paper proposes a structural framework to analyze firms’ voluntary participation in a price-freeze scheme under monopolistic competition. We develop a binary choice model under incomplete information that captures two distinct micro-founded interaction mechanisms: spatial competition and conformity to social norms, which are particularly relevant for the self-employed. We apply our game-theoretic framework to analyze the adoption of a novel pricing scheme offered to French balance-billing physicians, designed to freeze fees while compensating them through economic benefits. Our analysis leverages a unique geolocalized dataset covering the entire population of pediatricians, gynecologists, and ophthalmologists. We find compelling evidence of a significant preference for conformity, whereas competitive interactions appear to play a negligible role in physicians’ decision-making. These findings offer a strong rationale for the observed low adoption rate of this pricing regulation policy.
M. Lambotte, Heterogeneity in peer effects for binary outcomes. New Version (May 2026), Under Review.
I introduce heterogeneity into the analysis of peer effects arising from conformity by allowing peer-effect parameters to vary across agents’ actions. Using a structural model based on a simultaneous network game with incomplete information, I derive conditions that guarantee the uniqueness of the equilibrium and the identification of heterogeneous peer-effect parameters. Applying the model to data on smoking and alcohol consumption among secondary school students, and conducting policy simulations, I show that assuming a homogeneous preference for conformity leads to biased estimates of peer effects and ex ante policy evaluations
Work in progress
A. Houndetoungan and M. Lambotte, Asymmetries in Peer Effects for Continuous Outcomes. (Draft coming soon)
Substantial evidence shows that individuals tend to conform to their peers because deviating from peer behavior incurs a social penalty. We develop a structural model of peer effects with asymmetric conformity. Social penalties depend on whether individuals perform below or above each of their friends, generating distinct influences from high- and low-performing peers. The resulting game generalizes the standard conformity model but features non-differentiable best-response functions. Under reasonable conditions, we establish the existence and uniqueness of the equilibrium and show that the model is identified. We propose a GMM estimator that identifies both types of peer effects using friends' characteristics and exogenous predictions of their status as low- or high-performing peers as instruments. We illustrate the method using Add Health data and uncover diverse patterns of conformity across multiple outcomes. We then study the design of targeted interventions under limited resources. We find that ignoring asymmetries in peer effects leads to inefficient treatment assignment and substantial welfare losses, which may exceed the welfare losses that arise in the absence of social interactions.
M. Lambotte, J. Thuilliez and N. Touré, "Intergenerational Transmission of Smoking Behavior".
M. Lambotte and M. Tholimet, "Peer, Parents and ADHD: Network Formation, Parental Investments and Educational Outcomes".
S. Karimi and M. Lambotte, " Access to Care and Avoidable Consultations: The Redistributive Effects of e-Consultations".
M. Lambotte, “Demand systems with endogenous variety regime and corner solutions”. (A draft of the model and estimation strategy is available upon request.)
Modeling and estimating demand systems with differentiated products at a disaggregated scale is a challenging task due to the high number of corner solutions. I propose a discrete-continuous model that accounts for the endogenous formation of the consideration set. Consumers first choose their variety regime while being subject to cognitive and time costs. Then, they select the optimal non-negative (continuous) quantities of each variety-product pair. The model we propose is highly flexible as it accommodates the fact that consumers might never purchase some products, varieties or some variety-product pairs. This demand system is estimated on highly censored data from conventional and organic purchases, using the 2019 French Kantar WorldPanel.
Published Papers
Interactions
M. Lambotte, "Peer effects in binary outcomes: strategic complementarity and taste for conformity with endogenous network", Journal of Applied Econometrics, 2025. https://doi.org/10.1002/jae.3128
M. Lambotte, S. Mathy, A. Risch and C. Treibich, “Disentangling peer effects in transportation mode choice: the example of active commuting", Journal of Environmental Economics and Management, 2023. https://doi.org/10.1016/j.jeem.2023.102868
Media coverage: The Conversation
Quality food
M. Lambotte, S. De Cara, C. Brocas, and V. Bellassen, “Organic farming offers promising mitigation potential in dairy systems without compromising economic performances”, Journal of Environmental Management, vol. 334, 2023. https://doi.org/10.1016/j.jenvman.2023.117405
M. Lambotte, S. De Cara, C. Brocas, and V. Bellassen, “Carbon footprint and economic performance of dairy farms: The case of Protected Designation of Origin farms in France”, Agricultural Systems, vol. 186, 2021. https://doi.org/10.1016/j.agsy.2020.102979
M. Lambotte, S. De Cara, and V. Bellassen, “Once a quality food consumer, always a quality food consumer? Consumption patterns of organic, label rouge and geographical indications in French scanner data”, Review of Agricultural, Food and Environmental Studies, 2020. https://doi.org/10.1007/s41130-020-00121-z