Authors : Nurhasniza Idham Abu Hasan, Nor Azura Md. Ghani, Norazan Mohamed Ramli, Khairul Asri Mohd Ghani and Khairul Izan Mohd Ghani
Abstract: The most common way of analyzing prognostic factors in clinical data is by using Cox Proportional Hazard (PH) model. It is a well-recognized statistical technique for exploring the relationship between the survival of patient and several explanatory variables. The proportionality of the hazards is a critical assumption in the PH analysis and implies that the influence of covariates effect remains similar over time. However, this assumption is often violated. Therefore, different model should be used to deal with non-proportionality of hazards assumption. The aim of this study was to compare the Cox PH Model with non-PH Model as well as to identify the risk of death among Rheumatic Heart Disease (RHD) patients. In this study, we used secondary data in which a retrospective cohort study of 721 RHD patients that were obtained from University Kebangsaan Malaysia (UKM) and National Heart Institute (Institut Jantung Negara, IJN), Malaysia. Both Stratified Cox PH with and without non-PH covariate interaction were performed as non-PH Models. By using Akaike’s Information Criterion (AIC) and Deviance, the efficiency of the model performance were compared and then, the most suitable model was determined. Based on these values, the stratified Cox PH Model with no-interaction is the best model for RHD dataset. Five statistically significant prognostic factors that contribute to the risk of death among RHD patients were identified, namely those who diagnosed as emergency status (Opstatus), performed with mitral valve repair alone have Hypertension (HPT), redo operation (Opepisode) and had longer Coronary Pulmonary Bypass (CPB). The non-PH Models fit better than Cox PH Model with respect to the lowest for both deviance and AIC values. This stratified Cox PH Model serves as an alternative approach that can cope with the non-PH situation.
Nurhasniza Idham Abu Hasan, Nor Azura Md. Ghani, Norazan Mohamed Ramli, Khairul Asri Mohd Ghani and Khairul Izan Mohd Ghani, 2017. Rheumatics Heart Disease Using Stratified Cox Proportional Hazard Model with Time-Varying Covariate Effect. Journal of Engineering and Applied Sciences, 12: 9205-9209.