Table 3.

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

Variable	P-value	Category	Prevalence (n)	OR (95% CI)
Siblings with lice	<0.001	No	1.4% (3522)	1
		Yes	37.0% (27)	35.95 (13.90–93.01)
Hair thickness	0.418	Fine	1.1% (990)	1
		Medium	1.4% (1639)	1.04 (0.48–2.24)
		Thick	2.7% (920)	1.72 (0.77–3.87)
Hair colour	0.088	Light	0.9% (1962)	1
		Red	1.3% (77)	1.50 (0.19–11.63)
		Brown	2.1% (816)	2.14 (1.07–4.31)
		Black	3.3% (694)	2.39 (1.09–5.23)

Class and school affiliation were used as random variable with class nested in school. Total number of children was 3549 from 241 classes. ORs are in relation to the first category of each variable. Only variables significant at P < 0.15 in univariate analysis are included. Of those correlated (hair colour, family background, cares education and working hours: online Supplementary 1 and 2), only the strongest response (hair colour) is included in the model.

Random effect variance (CI): class = 0.24 (−0.42 to 0.90), P = 0.436; school = 0.08 (−0.28 to 0.44), P = 0.602.