Well-designed and well-conducted clinical studies represent gold standard approaches for generating medical evidence. However, elderly populations are systematically underrepresented in studies across major chronic medical conditions, which has hampered the generalizability (external validity) of studies to the real-world patient population. It is the norm that intervention studies often require a homogeneous cohort to test their hypotheses; therefore older adults with co-medications and comorbidities are often excluded. The purpose of this study is to assess the gap between clinical studies on comorbidities and prevalence in elderly populations derived from the National Health and Nutrition Examination Survey (NHANES) and the Multiparameter Intelligent Monitoring in Intensive Care II (MIMIC-II) dataset. A comorbidity gap between them was observed and reported in this work.