Table 3.

Prevalence odds ratios (PORs) and 95% confidence intervals of having eight or more headache days a month in the past three months for those expressing traffic noise-annoyance or insomnia

Predictor variable	N	POR	95% confidence intervals
			Lower limit	Upper limit
Day-time noise-annoyancea	2715	0.97	0.54	1.72
Night-time noise-annoyancea	2716	1.10	0.58	2.09
Insomniab	3011	2.12	1.08	4.15

^aAnswered with any of the following: somewhat, moderately, strongly, or extremely annoyed.^b Difficulty falling asleep or maintaining sleep, or early arousal on at least two nights a week during the past four weeks.