Exploring the Methodological Challenges of Investigating Comparison Groups with Different Underlying Characteristics: A Case Study

OBJECTIVE: To examine challenges in forming accurate conclusions from claims data when comparing different patient groups, and to stress the need to adjust for confounding variables through application of statistical methods. METHODS: Patients who were 60 or older and began amlodipine or felodipine in 1997 or 1998 were identified from a proprietary managed care claims database. Patients had 6 months of medical and outpatient pharmacy benefits coverage before and after initiating therapy. They were stratified on varying degrees of hypertension severity and on all-condition clinical complexity, and quantified with a proprietary Burden of Illness (BOI) score, defined as the expected resource use for the patients combined conditions during the 6 months before therapy. RESULTS: Of the 17,667 patients, 10,469 (59.3%) were female. The 12,389 amlodipine users were similar in age to felodipine users (n=5,278), 73 versus 74, respectively. More amlodipine users were assigned to the 2 most clinically complex quintile...