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Back to the Future: Modeling Time Dependence in Binary Data

Published online by Cambridge University Press:  04 January 2017

David B. Carter*
Affiliation:
Department of Political Science, Pond Laboratory 211, The Pennsylvania State University, University Park, PA 16802
Curtis S. Signorino
Affiliation:
303 Harkness Hall, Department of Political Science, University of Rochester, Rochester, NY 14627. e-mail: curt.signorino@rochester.edu
*
e-mail: dbc10@psu.edu (corresponding author)
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Abstract

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Since Beck, Katz, and Tucker (1998), the standard method for modeling time dependence in binary data has been to incorporate time dummies or splined time in logistic regressions. Although we agree with the need for modeling time dependence, we demonstrate that time dummies can induce estimation problems due to separation. Splines do not suffer from these problems. However, the complexity of splines has led substantive researchers (1) to use knot values that may be inappropriate for their data and (2) to ignore any substantive discussion concerning temporal dependence. We propose a relatively simple alternative: including t, t 2, and t 3 in the regression. This cubic polynomial approximation is trivial to implement—and, therefore, interpret—and it avoids problems such as quasi-complete separation. Monte Carlo analysis demonstrates that, for the types of hazards one often sees in substantive research, the polynomial approximation always outperforms time dummies and generally performs as well as splines or even more flexible autosmoothing procedures. Due to its simplicity, this method also accommodates nonproportional hazards in a straightforward way. We reanalyze Crowley and Skocpol (2001) using nonproportional hazards and find new empirical support for the historical-institutionalist perspective.

Information

Type
Research Article
Copyright
Copyright © The Author 2010. Published by Oxford University Press on behalf of the Society for Political Methodology 
Supplementary material: PDF

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Appendix

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