Table 2.

The Average Time Spent in Bed and the Total Number of Naps Taken during the Study, According to the Age and Schedule of the Drivers.^*

Driving Schedule	Younger Drivers	Older Drivers	All Drivers
All schedules
Average time in bed (hr)	5.34	5.03†	5.18
No. of drivers	40	40	80
Age (yr)	36±7	50±7	43±10
No. of naps	32	31	63
Steady day
Average time in bed (hr)	5.95	5.61	5.78‡
No. of drivers	10	10	20
Age (yr)	43±5	55±4	49±8
No. of naps	10	3	13
Advancing night
Average time in bed (hr)	5.27	4.93	5.10‡
No. of drivers	10	10	20
Age (yr)	34±6	53±5	44±11
No. of naps	3	10	13
Steady night
Average time in bed (hr)	4.58	4.16	4.37‡
No. of drivers	10	10	20
Age (yr)	32±6	49±7	40±11
No. of naps	11	11	22
Delaying evening
Average time in bed (hr)	5.55	5.40	5.47‡
No. of drivers	10	10	20
Age (yr)	33±4	43±5	38±7
No. of naps	8	7	15

^*Plus–minus values are means ±SD. A nap was defined as an episode of sleep outside the principal sleep period that could be scored with the use of electrographic criteria. The average age of the younger drivers was 36 years, and the average age of the older drivers was 50 years.

^†P=0.02 for the difference between age groups.

^‡P<0.001 for the difference with the other driving schedules, by analysis of variance.