Table 2.

Multivariate, mixed-effect logistic regression of reported head lice history (lice/no lice) in primary school children at 12 schools in Oslo, Norway

Variable	P-value	Category	Prevalence (n)	OR (95% CI)
Siblings with lice	<0.001	No	34.7% (2075)	1
		Yes	76.4% (398)	7.18 (5.41–9.52)
Sex	0.902	Female	45.4% (1284)	1
		Male	37.1%(1189)	0.98 (0.68–1.40)
Grade (age)	<0.001	Continuous		1.26 (1.18–1.35)
Hair thickness	<0.001	Fine	32.4% (744)	1
		Medium	42.5% (1127)	1.67 (1.32–2.11)
		Thick	50.5% (602)	2.18 (1.64–2.91)
Hair colour	0.570	Light	42.2% (1476)	1
		Red	47.1% (51)	1.17 (0.61–2.26)
		Brown	45.2% (557)	1.08 (0.85–1.38)
		Black	32.1% (389)	0.79 (0.48–1.32)
Hair type	0.018	Straight	40.2% (1861)	1
		Wavy	49.2% (439)	1.35 (1.06–1.74)
		Curly	34.7% (173)	0.79 (0.53–1.18)
Hair length	<0.001	Short	23.7% (1163)	1
		Medium	86.4% (339)	1.91 (1.41–2.60)
		Long	46.9% (971)	1.61 (1.05–2.47)
Family background	0.385	Norwegian	43.4% (1688)	1
		Western	42.9% (345)	0.91 (0.69–1.21)
		Developing	32.7% (440)	0.73 (0.45–1.16)
Working hours of mother	0.063	Short	43.4% (839)	1
		Long	40.4% (1634)	0.82 (0.67–1.01)
Working hours of father	0.209	Short	36.5% (457)	1
		Long	42.5% (2016)	1.18 (0.91–1.52)
Education of mother	0.914	Primary	32.6% (386)	1
		Secondary	39.2% (618)	1.05 (0.75–1.46)
		Higher	44.7% (1469)	1.07 (0.78–1.48)

Class and school affiliation were used as random variable with class nested in school. Total number of children was 2473 from 229 classes. ORs are in relation to the first category of each variable. All variables added were significant at P < 0.15 in univariate analysis.

Random effect variance (CI): class = 0.31 (0.14–0.48); P < 0.001, school = 0.12 (−0.01 to 0.25), P < 0.001.