Figure 7.

Comparison of interindividual differences in susceptibility to sleepiness due to SI and vulnerability to sleepiness during total sleep deprivation. The ordinate shows individual estimates of the magnitude of SI, relative to baseline sleepiness, expressed as difference from the group mean. The abscissa shows individual estimates of the effect of sleep deprivation, relative to baseline sleepiness, expressed as difference from the group mean. Both are in units on the KSS. Notice that the variability between individuals in the effect of SI on sleepiness is only somewhat smaller than the variability between individuals in the impact of sleep deprivation on sleepiness—however, the two effects are not significantly related within individuals.