Table 2. Factors associated with the length of the infestation-free period in randomized controlled trial of ivermectin treatment for head lice, Fortaleza, CE, Brazil, 2007.

Factor	Hazard ratioa	95% CI	P-value
Groupb	1.47	1.01–2.17	0.048
Sexc	1.95	1.21–3.11	0.005
Poverty index	1.41d	1.03–1.93	0.031
Crowding	1.06d	0.90–1.24	0.477
No. of sentinel children per household	1.11d	0.90–1.37	0.311

CI, confidence interval.
^a Result of Cox regression.
^b Control group versus intervention group. In the intervention group, all family members of sentinel children who lived in the same household as the children were treated with ivermectin; in the control group, no family member was treated.
^c Females versus males.
^d The hazard ratio indicates the effect of a whole unit increase in the unit of measurement.