Figure 2

Comparison of midpoint of sleep (mean + SD) among TT (n = 223), TC (n = 91) and CC (n = 14) subjects during weekdays (white circles) and weekends (black circles). During weekdays, the midpoint of sleep of CC subjects was significantly later than those of TT and TC subjects. During weekends, there was a significant difference in midpoint of sleep only between TC and CC subjects. *P < 0.05, **P < 0.01.