His primary focus is on the psychological, emotional, and clinical aspects involved in the decisions of relevant participants in a treatment decision. His research includes experimental simulation studies of medical treatment decisions involving risky options and uncertainty among older patients, as well as analyses of pre-collected data on clinical practice and patient outcomes. Hemmerich draws on his methodological and statistical expertise in the design and execution of all of his research projects as well as in educating students and fellows in the Section of Geriatrics and Palliative Medicine. The results of his work are applicable to improving the medical treatment of older patients.