Table 1.

Comparison of time series data among the OD (off-duty), 2NS (2 night shifts) and 4NS (4 night shifts) groups

Variables (mean ± SD)	Group ( n = 23, 20, 16)	Time 1	Time 2	Time 3	Time 4	F(2,56)	P- value
Sleep latency of MWT (min)	Off-duty	24.3 ± 7.6	26.1 ± 7.0	23.4 ± 9.4	22.0 ± 8.3	11.03	<0.001a
	Two night shifts	17.0 ± 13.1	22.1 ± 15.1	18.8 ± 12.9	16.3 ± 14.8
	Four night shifts	8.2 ± 6.9	11.0 ± 12.2	13.1 ± 11.6	10.1 ± 13.7
Sleep latency of MSLT (min)	Off-duty	13.2 ± 6.7	10.4 ± 6.4	8.6 ± 6.3	8.3 ± 5.9	1.18	0.314
	Two night shifts	10.0 ± 6.3	8.3 ± 6.1	8.0 ± 6.3	7.4 ± 5.2
	Four night shifts	7.5 ± 5.2	6.0 ± 4.6	8.5 ± 7.2	8.6 ± 7.4
State Anxiety Scale	Off-duty	39.7 ± 7.1	38.4 ± 6.8	36.5 ± 8.1	35.4 ± 8.5	5.18	0.009b
	Two night shifts	42.5 ± 8.0	43.6 ± 7.4	43.4 ± 7.3	42.2 ± 7.7
	Four night shifts	38.6 ± 7.0	36.8 ± 7.8	35.1 ± 7.5	33.9 ± 7.0
Stanford Sleepiness Scale	Off-duty	3.2 ± 0.2	3.5 ± 0.2	3.8 ± 0.2	4.1 ± 0.2	0.81	0.451
	Two night shifts	3.4 ± 1.0	3.7 ± 1.1	4.2 ± 1.3	4.3 ± 1.3
	Four night shifts	3.4 ± 1.0	3.4 ± 1.0	3.4 ± 1.0	3.9 ± 1.3
Wisconsin Card Sorting Test
Number of perseverative errors	Off-duty	11.6 ± 4.3	9.7 ± 2.9	10.7 ± 2.7	9.8 ± 2.5	0.98	0.383
	Two night shifts	12.1 ± 6.9	11.5 ± 6.4	12.1 ± 7.3	12.8 ± 11.0
	Four night shifts	9.9 ± 2.6	9.9 ± 1.9	10.25 ± 4.1	10.6 ± 3.1
Number of total errors	Off-duty	23.5 ± 7.2	20.7 ± 5.7	18.3 ± 4.9	17.2 ± 5.1	1.44	0.246
	Two night shifts	24.7 ± 14.0	22.4 ± 12.0	23.0 ± 12.5	24.0 ± 13.7
	Four night shifts	21.2 ± 5.2	19.6 ± 5.3	19.6 ± 5.6	18.2 ± 4.5

Abbreviations: MWT Maintenance of Wakefulness Test, MSLT Multiple Sleep Latency Test, SD standard deviation.

Scheffé’s post-hoc test: ^aOD group > 2NS group, OD group > 4NS group, 2NS group > 4ND group; ^bOD group < 2NS group, 4NS group < 2NS group.