VRIFA: a nonlinear SVM visualization tool using nomogram and localized radial basis function (LRBF) kernels

Prediction problems are prevalent in medical domains. For example, computer-aided diagnosis or prognosis is a key component in a CDSS (Clinical Decision Support System). SVMs, especially SVMs with nonlinear kernels such RBF kernels, have shown superior accuracy in prediction problems. However, they are not favorably used by physicians for medical prediction problems because nonlinear SVMs are difficult to visualize, thus it is hard to provide intuitive interpretation of prediction results to physicians. Nomogram was proposed to visualize SVM classification models. However, it cannot visualize nonlinear SVM models. Localized RBF (LRBF) kernel was proposed which shows comparable accuracy as the RBF kernel while the LRBF kernel is easier to interpret since it can be linearly decomposed. This paper presents a new tool named VRIFA, which integrates the nomogram and LRBF kernel to provide users with an interactive visualization of nonlinear SVM models. VRIFA graphically exposes the internal structure of nonlinear SVM models showing the effect of each feature, the magnitude of the effect, and the change at the prediction output. VRIFA also performs nomogram-based feature selection while training a model in order to remove noise or redundant features and improve the prediction accuracy. The tool has been used by biomedical researchers for computer-aided diagnosis and risk factor analysis for diseases. VRIFA is accessible at http://dm.postech.ac.kr/vrifa .