In this issue of Archives, Johnson et al1 report findings from a single-center observational study evaluating the relationship between early transfusion of fresh frozen plasma (FFP) and multiple organ failure. Although the authors appropriately label their findings' association in the title and prose, their recommendations clearly imply causation. Specifically, they call for a reexamination of policies aimed at early FFP transfusion. However, there is a key methodologic flaw in that this reexamination threatens the validity of this study and limits the conclusions we can draw from it.
Dimick JB, Livingston EH. Comparing Treatments Using Observational Study DesignsWhat Can We Do About Selection Bias?. Arch Surg. 2010;145(10):927. doi:10.1001/archsurg.2010.223