Table 1.

Sample characteristics

	Short, n (%)	Normal, n (%)	Long, n (%)
Sleep duration	7871 (23.6)	25 102 (75.3)	383 (1.1)
	Early, n (%)	Intermediate, n (%)	Late, n (%)
Chronotype	9235 (27.7)	20 911 (62.7)	3210 (9.6)
	Yes, n (%)	No, n (%)
Insomnia symptoms	10 438 (31.3)	22 918 (68.7)
Excessive daytime sleepiness	7564 (22.7)	25 792 (77.3)
Sleep medication use	90 (0.3)	33 266 (99.7)
Sleep apnoea	133 (0.4)	33 223 (99.6)
Psych. medication use	2016 (6)	31 340 (94.0)
Depressive symptoms	5914 (17.7)	27 442 (82.3)