Figure 1. Observed ratings of subjective sleepiness on the Karolinska Sleepiness Scale (KSS) plotted against time of day (at home base) with a LOWESS line indicating approximate means for home base time zone (left) and other time zones (middle) with the overall distribution of time zones for all ratings (right).

KSS ratings have had a random jitter applied to better illustrate the distribution at different levels.