Examples of simulated X-ray images of threat bags with typical hit rates (HR). A: gun with low target difficulty in the center (HR was 75%), B: knife with low target difficulty in upper right corner (HR was 56.5%), C: gun with high target difficulty in lower right corner (HR was 50%), D: knife with high target difficulty in lower left corner (HR was 32.5%). Reproduced from Basner M, Rubinstein J, Fomberstein KM, et al. Effects of Night Work, Sleep Loss and Time on Task on Simulated Threat Detection Performance. SLEEP 2008;31(9):1251–1259 (with permission)