Duration models and proportional hazards in political science

被引:257
作者
Box-Steffensmeier, JM [1 ]
Zorn, CJW
机构
[1] Ohio State Univ, Columbus, OH 43210 USA
[2] Emory Univ, Atlanta, GA 30322 USA
关键词
D O I
10.2307/2669335
中图分类号
D0 [政治学、政治理论];
学科分类号
0302 [政治学]; 030201 [政治学理论];
摘要
A key assumption of nearly all widely used duration models is that the hazard ratios (i.e., the conditional relative risks across substrata) are proportional to one another and that this proportionality is maintained over time. Estimation of proportional hazards models when hazards are nonproportional results in coefficient biases and decreased power of significance tests. Techniques for relaxing this assumption allow scholars to test whether the effects of covariates change over time and also permit a more nuanced understanding of the phenomenon being studied. We address the potential problems with incorrectly assuming proportionality, illustrate a number of tests for nonproportionality, and conclude with a discussion of how to accurately and efficiently estimate these models in the presence of nonproportional hazards. We investigate the proportionality assumption for Cox's semiparametric model in the context of the "liberal peace" debate, using data on international conflict in the postwar period.
引用
收藏
页码:972 / 988
页数:17
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