title: On penalized likelihood estimation for a non-proportional hazards regression model.
abstract: In this paper, a semi-parametric generalization of the Cox model that permits crossing hazard curves is described. A theoretical framework for estimation in this model is developed based on penalized likelihood methods. It is shown that the optimal solution to the baseline hazard, baseline cumulative hazard and their ratio are hyperbolic splines with knots at the distinct failure times.
authors.affiliation: Biostatistics & Bioinformatics Department, Fox Chase Cancer Center, Philadelphia, PA 19111.
authors.forename: Karthik
authors.initials: K
authors.lastname: Devarajan
authors.affiliation: Division of Statistics, Northern Illinois University, DeKalb, IL 60115.
authors.forename: Nader
authors.initials: N
authors.lastname: Ebrahimi
keywords: censored survival data analysis; crossing hazards; penalized likelihood; proportional hazards; spline