Table 2. Change from 8-hour shift system to 12-hour shift system and sleep, sleepiness and insomnia. Odds ratios (OR) with 95% confidence intervals in the GEE models with those who stayed in 8-hour shift system as the reference group.

	OR	95%CI	p-value
Habitual sleep length (h)	0.971	0.740–1.273	0.831
Sleep length before 1st morning shift	2.330	1.599–3.395	<0.001
Sleep length between morning shifts	1.890	1.419–2.518	<0.001
Sleep length before night shift	1.009	0.874–1.165	0.906
Sleep length after night shift (day sleep)	0.817	0.563–1.563	0.286
Sleep length after last night shift	1.203	0.875–1.653	0.256
Sleep length between days off	0.968	0.749–1.250	0.801
Sleepiness in morning shifts (often or always)	0.479	0.286–0.804	0.005
Sleepiness in night shifts (often or always)	0.554	0.315–0.975	0.040
Insomnia in relation to morning shifts (often or always)	0.941	0.551–1.607	0.824
Insomnia in relation to night shifts (often or always)	0.628	0.356–1.109	0.109
Sleepiness in morning shift (KSS 7 or more) 1	0.749	0.443–1.268	0.282
Sleepiness in night shift (KSS 7 or more) 1	1.113	0.649–1.909	0.697

GEE analyses adjusted with age, sex and baseline 8-hour shift system (fast forward vs. slow forward). ¹ Retrospectively rated sleepiness, KSS = Karolinska Sleepiness Scale.