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Thomas Peyrat publishes two new advances in applied probability
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Thomas Peyrat, PhD student at CREST-GENES and at Exiom Partners, in Finance-Insurance, has just reached a major milestone in his doctoral journey with the publication of his first paper in ESAIM: Probability and Statistics, as well as the release of a new working paper.

These two works, conducted in collaboration with his advisors Caroline Hillairet (ENSAE Paris – CREST) and Anthony Réveillac (INSA Toulouse – Toulouse Mathematics Institute), are part of his PhD carried out in partnership with Exiom Partners, a consulting firm actively involved in applied research.

🔹 A new Clark–Ocone formula for Poisson functionals
The first paper, titled A non-compensated Clark–Ocone formula for Poisson functionals, develops a decomposition formula for integrable Poisson functionals. This non-compensated version offers several technical advantages compared to the classical compensated approach, paving the way for new potential applications.
👉 Read the article in ESAIM: Probability and Statistics

🔹 Multivariate self-exciting processes with dependencies
The second work, currently available as a preprint, introduces a new class of multivariate self-exciting processes capable of modeling dependencies between event intensities and values. This modeling framework is particularly promising in insurance applications, for instance to capture links between claim frequency and severity.
👉 Read the preprint

We warmly congratulate Thomas for these important contributions, which highlight the strength of collaboration between academic research and industry, as well as the quality of doctoral training at CREST.

Contribution de Pierre Rousseaux à l’Investment Report 2024/2025 de la European Investment Bank (EIB)
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Pierre Rousseaux, doctorant au CREST-GENES, signe une contribution dans l’Investment Report 2024/2025 de la Banque Européenne d’Investissement (BEI) (Encadré C, Chapitre 5).

Dans un contexte de tensions géopolitiques croissantes, les dépendances commerciales de l’Union européenne deviennent un enjeu stratégique majeur. La guerre en Ukraine, la montée du protectionnisme aux États-Unis et la concentration des chaînes de valeur en Chine exposent l’UE à des risques accrus de perturbations d’approvisionnement. Quels sont les produits et secteurs les plus vulnérables ? Quelles sont les dépendances critiques ? Comment renforcer la résilience européenne ?

Dans cette contribution, Pierre Rousseaux explore ces questions sur une période plus étendue que celle abordée dans son précédent travail coécrit avec Isabelle Méjean pour le CEPR – Centre for Economic Policy Research. Voici les principales conclusions issues de son analyse pour la BEI :

  • Les vulnérabilités sont de plus en plus concentrées sur les importations chinoises
    La part de la Chine dans les dépendances commerciales de l’UE a significativement augmenté, tandis que celle des États-Unis et du reste du monde a diminué de 3 à 10 points de pourcentage.

  • Les dépendances en amont des chaînes de valeur sont les plus risquées
    Les vulnérabilités situées à plus de trois étapes du consommateur final représentent 49 % des produits critiques. Une rupture dans ces segments pourrait affecter l’ensemble des chaînes d’approvisionnement européennes.

  • Certaines dépendances sont structurellement critiques pour l’industrie européenne
    Les produits vulnérables se concentrent dans les secteurs de la chimie, des métaux et de la céramique — industries essentielles pour de nombreuses filières stratégiques.

  • Ces vulnérabilités sont persistantes
    41 % des dépendances commerciales identifiées avant la crise financière mondiale étaient encore présentes après celle-ci, et 35 % ont perduré à long terme, témoignant de leur caractère structurel et de la difficulté à s’en détacher.

  • Sur les 5 381 produits importés par l’UE, le nombre de vulnérabilités identifiées varie selon les critères retenus : entre 359 (avec les critères les plus larges) et 29 (selon les cinq critères les plus restrictifs définis avec Isabelle Méjean). Bien que ce chiffre puisse sembler faible, il regroupe des produits à risque extrême, caractérisés par :

    • une forte concentration des fournisseurs hors UE

    • une très faible production au sein de l’UE

    • une capacité de substitution quasi inexistante en cas de choc

Pourquoi est-ce crucial ?
Identifier précisément les dépendances et leurs risques permet de concevoir des politiques ciblées : diversification des fournisseurs, relocalisation, investissements stratégiques… Ces enjeux dépassent la sphère économique : ils ont un impact direct sur la souveraineté industrielle et technologique de l’UE.

Pierre Rousseaux propose également une page dédiée à ce sujet sur son site, qui croise les résultats de son papier avec Isabelle Méjean et ceux réalisés pour la BEI. Elle s’adresse aux publics académique, statistique et politique, et permet d’explorer les vulnérabilités commerciales de l’UE de manière approfondie :
https://www.pierrerousseaux.com/eu-trade-dependencies

Consulter le rapport complet ici.

Note IPP n°113 : Une étude éclaire l’ampleur du phénomène de la réembauche par le même employeur
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L’IPP publie ce mercredi 19 mars une étude consacrée à la question de la réembauche c’est-à-dire le processus par lequel des travailleurs précédemment licenciés ou temporairement au chômage sont rappelés par leur ancien employeur.

Retrouvez la note directement sur le site de l’Institut des Politiques Publiques ici.

Les enseignements principaux de cette étude sont les suivants:

  • Il s’agit d’un phénomène massif qui affecte tous les secteurs d’activité : les réembauches représentent environ 44 % de l’ensemble des embauches en France entre 2012 et 2019.
  • Les réembauches et le dualisme contractuel sont intimement liés : près de 93 % concernent des contrats à durée déterminée de courte durée, souvent inférieure à un mois.
  • La législation encadrant la réembauche ne semble que partiellement appliquée : plus d’un tiers des réembauches pourraient contrevenir au délai de carence obligatoire, et près de la moitié pourraient dépasser la limite légale de renouvellements.
  • Les réembauches concernent un groupe relativement restreint de travailleurs, dont un peu plus d’un quart subissent cinq réembauches ou plus par le même employeur chaque année. Elles sont également plus fréquentes chez les femmes et les travailleurs plus âgés;

Les auteurs de l’étude sont Olivier Charlot (professeur à CY Cergy Paris Université, chercheur au THEMA), Franck Malherbet (professeur à l’ENSAE Paris, chercheur affilié à l’IPP) et Eloïse Ménestrier est post-doctorante à la DARES.

Retrouvez également l’article du journal Le Monde : “une étude éclaire l’ampleur du phénomène de la réembauche par le même employeur”, qui se base sur la note IPP.

La réembauche de salariés, levier de précarisation des travailleurs | Alternatives Economiques

Beyond the PhD – CREST Series #3: Insights from PhD Supervisors
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At CREST, we aim to showcase the diverse career trajectories and perspectives of researchers who have navigated the path beyond their PhD. The “Beyond the PhD” series provides an opportunity to hear directly from experts across different fields about their experiences, challenges, and insights on life as a researcher.

For this third installment, we are featuring four distinguished researchers: Benoit Schmutz (Ecole polytechnique, IP Paris), Caroline Hillairet (GENES, ENSAE Paris, IP Paris), Paola Tubaro (CNRS, ENSAE Paris, IP Paris), and Nicolas Chopin (GENES, ENSAE Paris, IP Paris). Each of them shares their thoughts on the PhD journey, its impact on their careers, and the broader role of research in society.

Why pursue a PhD at CREST?

A PhD is much more than just academic training—it’s about developing a mindset that allows you to explore complex questions, think critically, and push the boundaries of knowledge. Our researchers highlight three key aspects that define the PhD experience at CREST:

🔹 An Environment for Intellectual Growth – A PhD is a journey of constant learning. You will develop a structured way of thinking, gain expertise in your field, and learn how to navigate uncertainty in research.

🔹 Opportunities for Interdisciplinary Work – At CREST, you will interact with researchers across economics, sociology, finance, and statistics, allowing for a dynamic and stimulating research experience.

🔹 A Supportive and Collaborative Research Culture – While research can be challenging, you will not be alone. Engaging with peers, supervisors, and the broader academic community is essential, and at CREST, we value collaboration as much as independence.

Watch the introduction to this series below.

Meet the Researchers

Each researcher featured in this edition brings a unique perspective on the PhD experience and beyond.

Benoit Schmutz – From PhD to Applied Economics

Benoit discusses how a PhD equips students with essential analytical skills, particularly in understanding labor markets and urban economics. He emphasizes the importance of rigor and adaptability in research.

🎥 Watch Benoit’s insights

Caroline Hillairet – Mathematics, Finance, and Research Opportunities

Caroline shares her journey from mathematics to finance, highlighting how a PhD opens doors to interdisciplinary research and the application of theoretical models to real-world problems.

🎥 Watch Caroline’s insights

Paola Tubaro – Networks, Society, and the Role of Research

Paola discusses how her research in computational social sciences evolved, emphasizing the collaborative nature of research and the impact of digital transformations on society.

🎥 Watch Paola’s insights

Nicolas Chopin – The Art of Asking the Right Questions

Nicolas talks about the role of uncertainty in research, how a PhD teaches resilience, and the impact of Bayesian statistics in various domains, including machine learning.

🎥 Watch Nicolas’s insights

Advice for Future PhD Students

If you are considering applying for a PhD at CREST, here are a few key takeaways from our researchers:

✅ Stay curious – Research is about exploration, so embrace new ideas and unexpected results.
✅ Engage with the academic community – Attend conferences, collaborate with other researchers, and actively participate in lab activities.
✅ Be patient and persistent – Progress in research takes time. Learning how to overcome obstacles is part of the PhD experience.
✅ Think beyond the thesis – Your PhD is not just about writing a dissertation; it’s about developing a way of thinking that will shape your career.

Check out our two previous series of Beyond the PhD on the CREST YouTube Channel:

Beyond the PhD – Series 1 – a video centered on the International Job Market from Economics PhD students.

Beyond the PhD – Series 2 – a series of videos from our PhD students on the definition of what is a PhD.

International Women’s Day: what progress for women in Economics?
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International Women Day 2025-2

March 8 is a global day celebrating the achievements of women in every domain. This day gives focus to issues such as gender equality, reproductive rights, and violence and abuse against women. Accordingly to its work, CREST is engaged in supporting women in research at all scale.

Gender inequalities in academic careers in Economics: situation report

As other disciplines, Economics is facing under representation from women, more specifically in more advanced levels in their academic career. According to data collected in 2023 and 2024 by the Women in Economics committee (WinE) from The French Economic Association (AFSE), the proportion of women varies considerably by hierarchical level.

  • At junior levels, women represent around 45% of workforce (lecturers, researchers, and post-doctoral fellows).
  • As they progress up the career ladder, the proportion of women falls drastically, to just 28% to 31% at the professorial level (university professors, CNRS research directors).
  • A regional disparity also exists in Île-de-France (Paris area), the proportion of women is lower than in province, more particularly in more advanced careers.

This phenomenon, commonly called “leaky pipeline”, enlightens the general issue for women to access the most prestigious positions and to progress towards them. Various factors can explain this situation: the weight of stereotypes, less recognition of women’s work, the often greater mental and family burden, as well as systemic barriers such as the lack of female role models and support networks.

Far from being a simple observation, these results led to practical initiatives to encourage women to pursue and grow in an academic career in Economics.

The WinE committee: one initiative to promote Women in Economics.

Facing those inequalities, the French Economic Association (AFSE) launched in 2023 the Women in Economics committee (WinE), nowadays chaired by Prof. Emmanuelle Taugourdeau (CNRS, CREST, Institut Polytechnique de Paris). First, the committee led a thorough study on gender distribution in academic careers in economics in France, inspired by works carried out in the US and in Europe.

In 2024, the committee took a further step forward with the introduction of a mentoring program, aimed at young economists at the start of their careers.

This program is based on a mentor / mentee relationship, where experienced researchers guide doctoral students and young researchers in their professional careers.

The first results are encouraging:

  • 90 mentors volunteered to the program, among them 56% of women, demonstrating a strong desire to support withing the profession.
  • 57 young researchers applied to the program, including 62% of doctoral students, 29% of postdoctoral fellows, and 9% of economists in early stages of their career.
  • 42 pairs were connected: mentees receive their mentor’s contact information and initiate the communication.

Initial feedback from mentors has been very positive: they emphasize the sense of usefulness, and the fact that they can share concrete advice on academic careers and professional challenges.

As for the mentees, several testimonials underline the importance of the feeling of trust and of having a point of reference in an environment sometimes perceived as competitive and solitary.

This program is part of a wider drive to strengthen the presence of women in the economics and facilitate their progress in advanced positions, such as Women in Economics from the European Economics Association, the Committee on the Status of Women on the Economics Profession (CSWEP) from the American Economic Association, or the CEPR Women in Economics Initiative.

Women in Economics at CREST

We are also working with our institutions to promote supportive policies, such as improved maternity leave and reduced teaching loads.

Crest has inherited a poor gender ratio from a historical hiring trend that did not consider gender diversity. It is crucial to actively address gender inequalities, as diversity not only benefits women but also enriches the range of perspectives within institutions. Crest is committed to making these efforts, and progress is already underway.

For instance, in Economics, the recent hiring process for assistant professors resulted in recruiting more women than men (four women versus three men). We are also working with our institutions to promote supportive policies, such as improved maternity leave and reduced teaching loads. Additionally, Crest members strive to foster a collegial and supportive environment to help women find their place in the lab. While this support is often implicit, we strongly believe that such attitudes are essential for enabling women to fully thrive in their roles.

CREST PhD voices from Claire Leroy and Marion Brouard, in their 4th year of PhD, they were on the international job market this year to start their professional academic journey.

In the longer-run, I hope to reach a position in academia which will allow me to participate in these initiatives not as a potential beneficiary but also as someone that can help future generations of women economists after me.

I think that such initiatives are great for women economists. I have heard about several of them during my PhD, but I have never participated in one. On a daily basis, I do not think too much about being a woman in economics right now. One reason why is because as a PhD student at CREST I have generally felt as well regarded as other PhDs regardless of gender and (at least in earlier cohorts when I arrived), there was mostly gender parity in terms of composition of the PhD. However, as a soon-to-be assistant prof, I definitely know (from the many reports and statistics that have been produced and from informal conversations) that there is a lot more struggle for women at the next stage of their academic career.

Therefore, in the future, I think that I will pay closer attention to initiatives like those developed by WinE and participate in it. For example, we know that the tenure track is a key and stressful period where an assistant prof needs to put up a lot of work. Because of the biological clock, this period also often coincides with the time when women will think about having kids if they want ones. While most universities now offer an extension of the tenure clock in this case, research still show that women are penalized with delayed tenure and increased exit of academia after parenthood (Lassen & Ivandic[1]). I believe that committees like WinE can help inform researchers about such important issues, come up with possible solutions and help make them enforced in the profession.

In the longer-run, I hope to reach a position in academia which will allow me to participate in these initiatives not as a potential beneficiary but also as someone that can help future generations of women economists after me.

[1] https://www.aeaweb.org/articles?id=10.1257/pandp.20241118

Beyond awareness, these initiatives help young women find colleagues they can relate to or role models—something that can be difficult in a field where women are still underrepresented.

I haven’t actively participated in Women in Economics initiatives before, partly because CREST has provided me with an inclusive and aware environment. Otherwise, I would have likely joined, and I don’t exclude doing so in the future, as I believe these associations can be incredibly valuable for young women in economics.

Economics remains a male-dominated field, particularly when moving up the academic ladder, and while awareness of gender disparities has grown, inequalities and discrimination still persist. Associations like Women in Economics play an important role in shedding light on these issues, providing a platform for women to speak up, and fostering a sense of community where young women feel heard and supported while not having to worry about how they are perceived. Beyond awareness, these initiatives help young women find colleagues they can relate to or role models—something that can be difficult in a field where women are still underrepresented. For some, having such figures to look up to can make a difference in believing that, as a young woman, you can be successful while staying true to yourself.

CREST at the IP Paris IA Action Summit: Exploring AI for Economic Forecasting and Algorithmic Optimization

On February 6, 2025, Institut Polytechnique de Paris hosted the IA Action Summit at École polytechnique, a high-level event bringing together leading researchers, industry experts, and policymakers to discuss the transformative role of artificial intelligence. Among the distinguished participants, Anna Simoni and Vianney Perchet, researchers at CREST, presented their latest work on AI applications in macroeconomic forecasting and algorithmic optimization, respectively.

Macroeconomic Nowcasting with AI and Alternative Data – Anna Simoni

Anna Simoni (CNRS, ENSAE Paris, École polytechnique, Hi!Paris Fellow), presented her work on integrating artificial intelligence and alternative data to improve macroeconomic nowcasting. She addressed the challenge of forecasting key economic indicators such as GDP growth, inflation, and financial cycles in real time—an essential task for policymakers, financial institutions, and businesses.

Her research highlights the potential of AI to handle large, complex, and mixed-frequency datasets from both traditional (e.g., national statistics, financial markets) and non-traditional sources (e.g., Google search data, satellite imagery, mobile phone traffic, credit card transactions). By applying machine learning techniques, including dynamic factor models, neural networks, and Bayesian methods, her work demonstrates how AI-driven models can enhance nowcasting accuracy, detect economic shifts early, and provide better insights into economic trends.

Through real-world applications, including an analysis of Google search data for GDP nowcasting, her findings reveal that AI methods can significantly improve short-term economic predictions, especially in periods of high uncertainty or economic recessions. However, she also emphasized that AI models must be carefully designed to ensure interpretability and reliability, as pure data-driven approaches do not always outperform traditional methods.

AI-Powered AI: Enhancing Algorithmic Decision-Making – Vianney Perchet

Vianney Perchet, (GENES, Hi!Paris Fellow), introduced the concept of AI-powered AI, where artificial intelligence assists and improves algorithmic decision-making in various fields, from optimization to reinforcement learning and recommender systems.

He explored how AI-oracles—AI systems that provide tentative solutions to computational tasks—can be leveraged to accelerate decision-making processes. Through examples like binary search with AI hints, he demonstrated the trade-offs between consistency and robustness: algorithms must be able to trust AI-generated predictions when they are accurate but remain resilient when faced with imperfect or misleading information.

Perchet highlighted several fundamental challenges in AI-assisted algorithms, including:

  • Strategic AI usage: AI-oracle calls can be costly, requiring efficient selection mechanisms.
  • Combination of multiple AI sources: Different AI models may offer varying predictions, requiring aggregation methods to improve reliability.
  • Incentivization: AI models may have their own objectives, necessitating mechanisms to align them with user needs.
  • Learning from structure: AI-assisted algorithms must adapt and refine predictions over time for better long-term performance.
  • Beyond worst-case scenarios: Moving beyond rigid worst-case analyses toward realistic, instance-dependent performance guarantees.

His research opens exciting new perspectives for integrating AI into optimization problems, online learning, and algorithmic decision-making, with applications ranging from robotics and computer vision to financial forecasting and recommender systems.

CREST’s Commitment to AI Research

CREST’s involvement in the IP Paris IA Action Summit, through the contributions of Anna Simoni and Vianney Perchet,demonstrates the lab’s strong engagement in artificial intelligence research applied to economics, forecasting, and decision-making. Their work aligns with ongoing research at CREST on machine learning, reinforcement learning, and statistical AI methods, led by scholars such as Nicolas Chopin, Paola Tubaro, Bruno Crépon, and Olivier Gossner.

As AI continues to transform economic modeling and optimization, CREST continues its research of exploring how AI can enhance forecasting, decision processes, and strategic learning in uncertain environments.