Publications by Year: 2014

2014
Chuang J, Wilkerson JD, Weiss R, Tingley D, Stewart BM, Roberts ME, Poursabzi-Sangdeh F, Grimmer J, Findlater L, Boyd-Graber J, et al. Computer-Assisted Content Analysis: Topic Models for Exploring Multiple Subjective Interpretations. Advances in Neural Information Processing Systems Workshop on Human-Propelled Machine Learning. 2014.Abstract

Content analysis, a labor-intensive but widely-applied research method, is increasingly being supplemented by computational techniques such as statistical topic modeling. However, while the discourse on content analysis centers heavily on reproducibility, computer scientists often focus more on increasing the scale of analysis and less on establishing the reliability of analysis results. The gap between user needs and available tools leads to justified skepticism, and limits the adoption and effective use of computational approaches. We argue that enabling human-in-the-loop machine learning requires establishing users’ trust in computer-assisted analysis. To this aim, we introduce our ongoing work on analysis tools for interac- tively exploring the space of available topic models. To aid tool development, we propose two studies to examine how a computer-aided workflow affects the uncovered codes, and how machine-generated codes impact analysis outcome. We present our prototypes and findings currently under submission. 

nipshpml2014.pdf
Coppola A, Stewart BM. lbfgs: Efficient L-BFGS and OWL-QN Optimization in R. 2014.Abstract

This vignette introduces the lbfgs package for R, which consists of a wrapper built around the libLBFGS optimization library written by Naoaki Okazaki. The lbfgs package implements both the Limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) and the Orthant-Wise Limited-memory Quasi-Newton (OWL-QN) optimization algorithms. The L-BFGS algorithm solves the problem of minimizing an objective, given its gradient, by iteratively computing approximations of the inverse Hessian matrix. The OWL-QN algorithm finds the optimum of an objective plus the L1 norm of the problem’s parameters. The package offers a fast and memory-efficient implementation of these optimization routines, which is particularly suited for high-dimensional problems. The lbfgs package compares favorably with other optimization packages for R in microbenchmark tests.

lbfgsvignette.pdf
Structural topic models for open-ended survey responses
Roberts ME, Stewart BM, Tingley D, Lucas C, Leder-Luis J, Gadarian S, Albertson B, Rand D. Structural topic models for open-ended survey responses. American Journal of Political Science. 2014;58 :1064-1082.Abstract

Collection and especially analysis of open-ended survey responses are relatively rare in the discipline and when conducted are almost exclusively done through human coding. We present an alternative, semi-automated approach, the structural topic model (STM) (Roberts, Stewart, and Airoldi 2013; Roberts et al. 2013), that draws on recent developments in machine learning based analysis of textual data. A crucial contribution of the method is that it incorporates information about the document, such as the author’s gender, political affiliation, and treatment assignment (if an experimental study). This article focuses on how the STM is helpful for survey researchers and experimentalists. The STM makes analyzing open-ended responses easier, more revealing, and capable of being used to estimate treatment effects. We illustrate these innovations with analysis of text from surveys and experiments.

topicmodelsopenendedexperiments_0.pdf ajpsappendix.pdf

Awarded the Gosnell Prize for Excellence in Political Methodology for the best work in political methodology presented at any political science conference during the preceding year.  Data at: http://dx.doi.org/10.7910/DVN/29405