Fall Semester 2025-2026

Title: Refugees and entrepreneurship: Evidence from Ukrainians in Poland (with Cevat Giray Aksoy and Piotr Lewandowski)

Speaker:  Professor Pierre-Louis Vezina, ​King's College London

Host:  Assistant Professor Kospentaris Ioannis, Department of Economics, Athens University of Economics and Business

Time: 15.30 -17.00

Room:  76, Patission Str., Antoniadou Wing, 3rd floor, Room A36

Title: ""Bayesian binary classification under label uncertainty with network-informed Gaussian Processes""

Speaker: Postdoctoral Researcher Konstantinos Bourazas, Department of Economics, Athens University of Economics and Business.

Host:  Assistant Professor Alexopoulos Angelos, Department of Economics, Athens University of Economics and Business

Time: 15.30 -17.00

Room:  76, Patission Str., Antoniadou Wing, 3rd floor, Room A36

Abstract: We study Bayesian binary classification under one-sided (positive-only) label noise—known as positive–unlabeled (PU) learning—with both covariate and multi-layer network data. We combine these modalities through a Product-of-Experts (PoE) model, where each expert handles one data source, the latent logits combine additively, and the likelihood accounts for missed positives via a false-negative rate η. Our main contributions are: (i) identifiability under mild calibration conditions; (ii) posterior contraction of the latent function at the near-minimax nonparametric rate; and (iii) parametric $n^{-1/2}$ contraction for η. We show the PoE model is distributionally equivalent to a single Gaussian process with composite covariance, and that expert agreement tightens finite-sample bounds. We develop a bespoken Markov chain Monte Carlo algorithm to estimate under the Bayesian paradigm this PU–PoE setting, proving scalability as the number of experts grows. Empirically, our method outperforms strong PU baselines and proves useful in real fuel-tax fraud detection data from the Greek economy, providing calibrated uncertainty for decision support.

Title: "Resource Risk and the Origins of Inequality: Evidence from a Pastoralist Economy"
(co-authored with Konstantinos Angelopoulos, Rebecca Mancy, Dorice Agol, Elissaios Papyrakis)

Speaker: Assistant Professor Spyridon Lazarakis, Lancaster University

Host:  Assistant Professor Alexopoulos Angelos, Department of Economics, Athens University of Economics and Business

Time: 15.30 -17.00

Room:  76, Patission Str., Antoniadou Wing, 3rd floor, Room A36

Attachments:  PDF of Relevant Paper

Abstract: Resource risk is a core ingredient of models of wealth inequality in modern economies, but remains understudied in explanations of inequality in early human and small-scale societies that can inform us about the origins of inequality. Resource risk generates variation in resources and leads to wealth inequality via savings decisions, given the available production and storage technology and the institutional arrangements that govern property rights and insurance. We examine whether this mechanism can explain wealth inequality in a pastoralist economy where wealth is held in livestock, production and storage technology resembles that of early human societies and there is virtually no financial market penetration. Our analysis uses original survey data from traditional Turkana pastoralist communities in Kenya to measure wealth inequality and relevant shocks to resources and to inform a model of wealth accumulation under resource risk. The data reveal substantial wealth inequality and resource risk, including via shocks to the growth rate of livestock holdings, which depends on droughts. Asset accumulation decisions also show that livestock is not used as a buffer stock with respect to shocks to livestock. The wealth accumulation model accurately reproduces the empirical wealth distribution while also predicting the pattern of asset accumulation decisions in response to different shocks to resources observed in the data. These results demonstrate that resource risk and the economic decision making it implies explain the wealth inequality observed in the Turkana pastoralist economy we study. Our findings highlight the role of the resource risk mechanism as a driver of inequality in a small-scale economy, suggesting its importance in the origins of inequality in early human societies.

Title: "Perfect Secrecy in the Wild: A Characterization"  
(co-authored with Massimiliano Furlan & Alkis Georgiadis-Harris)

Speaker: Associate Professor Costas Cavounidis, University of Warwick

Host:  Assistant Professor Efthymios Athanasiou, Department of Economics, Athens University of Economics and Business

Time: 15.30 -17.00

Room:  76, Patission Str., Antoniadou Wing, 3rd floor, Room A36

Abstract: Alice wishes to reveal the state X to Bob, if he knows some other information Y also known to her. If Bob does not, she wishes to reveal nothing about X at all. When can Alice accomplish this? We provide a simple necessary and sufficient condition on the joint distribution of X and Y. Shannon's result on the perfect secrecy of the one-time pad follows as a special case. Further, we characterize what information about X can be revealed to Bob when he knows Y, a characterization valid even when our main condition fails. We discuss implications for algorithmic fairness and digital privacy regulation generally.