Hans Ligtenberg and Gerjan Zwiers win FEB Research Awards 2025

The awards for best PhD thesis and best graduate of the research master were presented at the Faculty of Economics and Business’ (FEB) annual PhD conference, which was held recently. Hans Ligtenberg won the best PhD Thesis Award 2025 for his thesis on estimation and inference with weak instrumental variables. Gerjan Zwiers won the Research Master Graduate Award for his research on the effect of unilateral divorce laws on children’s later-life.

Best PhD Thesis Award 2025

Hans Ligtenberg obtained his PhD degree in July 2025. His thesis titled ‘Estimation and inference with many and weak instrumental variables’ was supervised by Professor Aico van Vuuren and Associate Professor Tom Boot. In his thesis, Ligtenberg developed methods to reliably estimate and test causal effects using instrumental variable (IV) models with many, potentially weak IVs. The first chapter of his thesis, which was co-authored by Boot, was published in the Journal of Econometrics. It considers the widely used Generalized Method of Methods (GMM) in a notoriously difficult setting. The paper highlights empirical settings where the theory is relevant, proves a new central limit theorem, and uses this to analyze the effect of the concentration of financial activities in banks on systemic risk.

The second chapter of Ligtenberg’s thesis was nominated for the best PhD paper award at the 2024 conference of the International Association for Applied Econometrics (IAAE). In it, he generalized the tests developed in the first chapter and the previously developed jackknife type tests to clustered data. The third chapter of his thesis was co-authored by Professor Tiemen Woutersen following a research visit to the University of Arizona. It focuses on multidimensional clustering in judge designs, a combination of two highly active research areas. The paper demonstrates that multidimensional clustering in judge designs induces bias in commonly used estimators and provides feasible corrections. Given the popularity of judge designs in evaluating judicial decisions, bail policies, and administrative rulings, this contribution is highly relevant.

By addressing mismatches between econometric theory and empirical practice, Ligtenberg’s thesis further improves the reliability of applied economic research and policymaking. His supervisors state that, with the econometric theory, simulations and empirical applications he has developed, Ligtenberg has produced work that goes well beyond what is typically expected within a PhD trajectory. His thesis was thus rewarded a cum laude distinction. Ligtenberg is currently a postdoctoral researcher in econometrics at the Erasmus University Rotterdam.

Research Master Graduate Award

Gerjan Zwiers graduated Summa Cum Laude from the Research Master in Economics & Business in 2025 and is now working as a PhD candidate at FEB. Apart from his research master, Zwiers also obtained a joint master’s degree in Economics and Finance, where he also graduated with highest honors. His research master’s thesis titled ‘The Effect of Unilateral Divorce Laws on Children’s Later-Life Outcomes: Does it Run Through Divorce?’ was supervised by Associate Professor Bertrand Achou. Using survey data from the The Panel Study of Income Dynamics (PSID), Zwiers studied the effects of unilateral divorce laws (UDLs) in the U.S. on late-life outcomes of children, such as earnings, educational achievement, and various health-related factors. His research shows that childhood exposure to unilateral divorce laws reduces educational attainment and worsens health in adulthood, but that this likely does not occur through parental divorce.

According to Achou, Zwier’s thesis demonstrates great skills for data construction. “The PSID’s unique structure makes it extremely interesting but also particularly difficult to use when one wants to connect different generations. Zwiers is extremely careful and thorough when it comes to data construction. Combining datasets and creating variables very meticulously, he always raised the relevant issues. This is reflected in the thoroughness of his robustness checks.” Achou adds that Zwiers demonstrates a mastery of econometrics and causal inference techniques, and is very precise and careful regarding the interpretation of his results.