The authors retract the 15 February 2006 paper cited above because they have been unable to reproduce the results that were performed independently by the first author, Anil Potti, regarding validation of predictive models for thrombotic phenotypes. It has also been recognized that multiple samples appear to be duplicated in the training and validation datasets pertaining to the analysis presented in Figure 2 of the paper, which was also performed by Anil Potti. Since these results are fundamental to the conclusions of the paper, the authors formally retract the paper. The authors deeply regret the impact of this action on the work of other investigators and apologize to the readers, reviewers, and editors of Blood.