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Stat Med. 1994 May 30;13(10):1045-62.

Assessing time-by-covariate interactions in proportional hazards regression models using cubic spline functions.

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Department of Patient Studies, University of Texas M.D. Anderson Cancer Center, Houston 77030-4095.


Proportional hazards (or Cox) regression is a popular method for modelling the effects of prognostic factors on survival. Use of cubic spline functions to model time-by-covariate interactions in Cox regression allows investigation of the shape of a possible covariate-time dependence without having to specify a specific functional form. Cubic spline functions allow one to graph such time-by-covariate interactions, to test formally for the proportional hazards assumption, and also to test for non-linearity of the time-by-covariate interaction. The functions can be fitted with existing software using relatively few parameters; the regression coefficients are estimated using standard maximum likelihood methods.

[Indexed for MEDLINE]

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