1. Co-morbid disease and cancer: the need for more relevant conceptual models in health services research;Geraci;J Clin Oncol,2005
2. Prognostic importance of comorbidity in a hospital-based cancer registry;Piccirillo;JAMA,2004
3. Bang D Piccirillo JF Littenberg B Johnston A The adult co-morbidity evaluation-27 (ACE-27) test: a new co-morbidity index for patients with cancer 2000
4. Co-morbidity data collection form [Internet] Clinical Outcomes Research Office Website, Department of Otolaryngology, Washington University School of Medicine, St Louis, MO oto2.wustl.edu/clinepi/comorbid.html
5. How to measure co-morbidity: a critical review of available methods;Groot;J Clin Epidemiol,2003