Research Paper: External Validation of EPICON: A Grouping System for Estimating Morbidity Rates Using Electronic Medical Records. - Marion C. J. Biermans; Geert H. Elbers; Robert A. Verheij; Willem Jan van der Veen; Gerhard A. Zielhuis; Pieter de Vries Robbé (J. Am. Medical Informatics Assoc., 2008)