Dear Applied Statistics Workshop Community, Our next meeting of the semester will be on November 2 (12:00 EST). Edward Kennedy will present "Doubly robust capture-recapture methods for estimating population size." Please note that this meeting will take a hybrid format. Professor Kennedy will join us on Zoom, but we will gather in CGIS K354 (I will use the projection screen in K354 to display the Zoom window). Lunch will be provided. <Where> Hybrid: CGIS K354 or Zoom Bagged lunches are available for pick-up at 11:40 (CGIS K354). Zoom: https://harvard.zoom.us/j/99181972207?pwd=Ykd3ZzVZRnZCSDZqNVpCSURCNnVvQT09 <Abstract> Estimation of population size using incomplete lists (also called the capture-recapture problem) has a long history across many biological and social sciences. For example, human rights and other groups often construct partial and overlapping lists of victims of armed conflicts, with the hope of using this information to estimate the total number of victims. Earlier statistical methods for this setup either use potentially restrictive parametric assumptions, or else rely on typically suboptimal plug-in-type nonparametric estimators; however, both approaches can lead to substantial bias, the former via model misspecification and the latter via smoothing. Under an identifying assumption that two lists are conditionally independent given measured covariate information, we make several contributions. First, we derive the nonparametric efficiency bound for estimating the capture probability, which indicates the best possible performance of any estimator, and sheds light on the statistical limits of capture-recapture methods. Then we present a new estimator, and study its finite-sample properties, showing that it has a double robustness property new to capture-recapture, and that it is near-optimal in a non-asymptotic sense, under relatively mild nonparametric conditions. Next, we give a method for constructing confidence intervals for total population size from generic capture probability estimators, and prove non-asymptotic near-validity. Finally, we study our methods in simulations, and apply them to estimate the number of killings and disappearances attributable to different groups in Peru during its internal armed conflict between 1980 and 2000. <2022 Schedule> GOV 3009 Website: https://projects.iq.harvard.edu/applied.stats.workshop-gov3009 Calendar: https://calendar.google.com/calendar/embed?src=c_3v93pav9fjkkldrbu9snbhned8… Best, Shusei