Published online by Cambridge University Press: 26 September 2018
Complex models are of increasing interest to social scientists. Researchers interested in prediction generally favor flexible, robust approaches, while those interested in causation are often interested in modeling nuanced treatment structures and confounding relationships. Unfortunately, estimators of complex models often scale poorly, especially if they seek to maintain interpretability. In this paper, we present an example of such a conundrum and show how optimization can alleviate the worst of these concerns. Specifically, we introduce bigKRLS, which offers a variety of statistical and computational improvements to the Hainmueller and Hazlett (2013) Kernel-Regularized Least Squares (KRLS) approach. As part of our improvements, we decrease the estimator’s single-core runtime by 50% and reduce the estimator’s peak memory usage by an order of magnitude. We also improve uncertainty estimates for the model’s average marginal effect estimates—which we test both in simulation and in practice—and introduce new visual and statistical tools designed to assist with inference under the model. We further demonstrate the value of our improvements through an analysis of the 2016 presidential election, an analysis that would have been impractical or even infeasible for many users with existing software.
Authors’ note: Authors, who have contributed equally to this project, are listed alphabetically. This project has benefited immensely from feedback at the Stanford University Statistics Seminar, April 18, 2017; useR! 2016, hosted by Stanford University; American Political Science Association 2016; the International Methods Colloquium, hosted by Justin Esarey on November 11, 2016; the Stevens Institute of Technology on February 27, 2017; and the Bay Area R Users Group Official Meetups, hosted by Treasure Data (May 2016), Santa Clara University (October 2016), and GRAIL (June 2017). Thanks in particular to Susan Holmes, Joseph Rickert, Stefan Wager, Stephen Jessee, Christopher Wlezien, Trevor Hastie, Christian Fong, Luke Sonnet, Chad Hazlett, Kristyn Karl, Jacob Berman, Jonathan Katz, Gaurav Sood, Maraam Dwidar, and anonymous reviewers for additional comments (mistakes, of course, are ours). Pete Mohanty thanks Stanford University’s Vice Provost for Undergraduate Education for research leave. For replication materials, see Mohanty and Shaffer (2018).
Contributing Editor: Jonathan N. Katz