The prognostic score, or disease risk score (DRS), is a summary score that is used to control for confounding in non-experimental studies. While the DRS has been shown to effectively control for measured confounders, unmeasured confounding continues to be a fundamental obstacle in non-experimental research. Both theory and simulations have shown that in the presence of unmeasured confounding, c...

Outcomes studies of infections with resistant bacteria often do not account appropriately for intermediate variables--events in the causal pathway between the exposure and the outcome--when controlling for confounders. We discuss how failure to distinguish between confounders and intermediate variables can bias the analysis, and we address methods of approaching this issue.

206 AJCC AMERICAN JOURNAL OF CRITICAL CARE, May 2007, Volume 16, No. 3 www.ajcconline.org Beware of Transfusion-Related Confounders in Studies on Packed Red Blood Cells Gould and colleagues provide an excellent review of the limitations of packed cell transfusion in the intensive care unit. I applaud their efforts to painstakingly summarize evidence on a topic of widespread occurrence that is e...

Studies have associated statin use with increased risk of diabetes and diabetic complications. These studies often ensure comparability of statin users and non-users at baseline; however, most studies neglect to consider confounders that occur during follow-up. Failure to consider these confounders, such as new medications or procedures, may result in identification of a spurious association be...