Stein PD, et al. - This study draws on data from the Premier Healthcare Database to evaluate mortality with inferior vena cava (IVC) filters in unstable patients with pulmonary embolism using a design that eliminated immortal time bias. Researchers involved unstable subjects with pulmonary embolism and an admitting diagnosis of pulmonary embolism as well as a primary diagnosis of pulmonary embolism. Only when the filter was inserted on the first or second day of admission did mortality in unstable patients with pulmonary embolism seem to be reduced with IVC filters. They reported that the design used for these analyses controlled for immortal time bias as a cause of the lower mortality with IVC filters.