Increase in lifetime adverse drug reactions, service utilization, and disease severity among patients who will start COX-2 specific inhibitors: quantitative assessment of channeling bias and confounding by indication in 6689 patients with rheumatoid arthritis and osteoarthritis.

Abstract

Confounding by indication and channeling bias result in an overall increase in severity of about 25% for the above measures. Observational studies should account for these biases by a broadly defined propensity score that includes the variables identified in this report. These observations are germane to observational studies of disease modifying antirheumatic drugs and biologics, as well, and suggest the need for careful control of confounders when assessing treatment effects in rheumatic disease observational studies.