Table 7.

Effect of time of day on momentary alertness and cognitive throughput.^a

Feature	Effect on alertness	P value		Effect on cognitive throughput	P value
Time of day	Alertness varies sinusoidally with time of day, with an acrophase at 10:24 (09:26 to 11:21)	<.001	Cognitive throughput varies sinusoidally with time of day, with an acrophase at 09:19 (08:13 to 10:26)		<.001
Internal time	Alertness varies sinusoidally with internal time, with an acrophase at 14:24 (13:20 to 15:31)	<.001	Cognitive throughput varies sinusoidally with internal time, with an acrophase at 13:20 (12:02 to 14:38)		<.001

^aThe acrophase of the 24-hour circadian rhythm of cognitive performance is reported in hh:mm format with the corresponding 95% confidence intervals and P values.