Verification of the Assumptions of the Cox Model. Case Study: Venezuelan commercial banks, 1996-2004

The proposal of mathematical models needs in almost all the cases the verification of some assumptions. The Cox model is a regression model for survival data. The use of the Cox model without performing the verification of the assumptions is a common practice. In this paper, we present the methodology that should be followed to perform the verification of the four main assumptions of the Cox model, and it is only after this verification that we can be sure that the model is valid. This methodology is used to verify the assumptions and, in consequence, the validity of the Cox model in which the four finance ratios that describe the risk of fusion in the commercial banks in Venezuela, between 1996 and 2004 are identified.