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How Much Did Biases in the Study of Chronic Obstructive Pulmonary Disease Medications and Mortality Affect the Outcome?
- Nicholas J. Gross, MD, PhD
- From Loyola University Chicago Stritch School of Medicine, Maywood, IL 60153.
TO THE EDITOR:
Despite its very large data base, the study by Lee and colleagues (1) has problems that are inherent to observational data analyses in which potential confounding factors cannot be reliably controlled for. Of particular concern in their study is the absence of data about disease severity and smoking status, which the authors acknowledge. Attempts to adjust for these confounders by reference to a small pilot study of questionable relevance (2) or by internal “measures of disease severity” that are not described in any detail are not …
