Lucas GIRARD
Ph.D. Candidate in Economics
 Address: 5 avenue Henry Le Chatelier, Palaiseau, 91120, France
 Office: 4097
 Phone: +33 (0)1 70 26 69 43
 Email: lucas.girard[at]ensae.fr
 Personal Website: https://faculty.crest.fr/lgirard/
Biography
I am a thirdyear Ph.D. candidate in Economics at CREST (Center for Research in Economics and Statistics) under the supervision of Xavier D’Haultfoeuille.
I was born and I am still living in Paris. After my high school, I entered the French system of classes préparatoires studying two years in B/L at Henri IV (Paris), a formation that epitomizes multidisciplinary approaches (mathematics, economics, sociology, languages, history, geography, literature, philosophy). I passed entrance exams into French grandes écoles and then followed a fouryear double degree program between HEC Paris and ENSAE. I have started my Ph.D. since September 2017.
I am interested in econometric theory and its application. My current research is devoted to two main themes.
First, I wonder how to construct reliable measures of polarization, namely indices that quantify to which extent two exogenous groups tend to make different choices among a set of options. This abstract problem encompasses various practical settings: residential or school segregation between, for instance, natives and immigrants; speech polarization between Democrats and Republicans; buyers’ choices for different goods, etc. In particular, I investigate situations of “highdimensional choices”, that is when the number of observed choices in the data is low relative to the total number of distinct options. In such cases, natural measures of polarization suffer from a “smallunit bias”. As a consequence, other methods need to be developed to yield measures that can reliably be compared over time or across different settings. I currently have two projects in this direction, joint works with Xavier D’Haultfoeuille and Roland Rathelot: (i) the Stata package “segregsmall” implements three methods to estimate segregation indices in the context of small units; (ii) we propose an alternative method to Gentzkow, Shapiro, and Taddy (Econometrica 2019) to study speech polarization in the US Congress between Republican and Democrat speakers (18732016).
My second theme of research deals with the construction of nonasymptotic confidence intervals (CIs), i.e. whose probability to contain the target parameter is larger or equal to their nominal level for any sample size. It happens that the prevalent way to conduct inference in applied economics stems from asymptotic results. As a case in point, the CIs for the individual coefficients of a linear regression rely on the asymptotic normality of the tstatistic. Their properties are therefore only asymptotic. The validity of inference for any real finite sample involves an asymptotic approximation, which might be questioned in some settings. Hence the potential interest of nonasymptotic CIs. With Alexis Derumigny and Yannick Guyonvarch, we first studied such CIs for ratios of expectations. Retrospectively, that project appears as a kind of training exercise for a more ambitious and ongoing work about nonasymptotic CIs for individual coefficients of linear regression models.
Last but not least, I like teaching and think it is a vital complement to research and how to communicate and convey it. I have taught as a teacher assistant for econometrics and statistics courses at ENSAE.
Research Interests

Econometrics Econometric Theory

Economics Applied Microeconometrics

Statistics Natural Language Processing