Mean illness bouts, mean duration of illness, and mean illness-related absences
by sex and academic level, with mean weeknight total sleep time from January to
May shown as a continuous variable. The left-hand graph shows
9th/10th graders, while the right-hand graph shows
11th/12th graders. Open circles represent males, and
filled circles represent females. Dotted lines show a line of best fit for
males, while solid lines show a line of best fit for females.