Impact of a countywide smoke-free workplace law on emergency department visits for respiratory diseases: a retrospective cohort study

Table 2 Segmented poisson regression results ^*

	Monthly trend before law was passed (β₁)	Step change when law took effect (β₂)	Change in trend after law took effect (β₃)	Monthly trend after law took effect (β_{1 +}β₃)
COPD
β (SE)	-0.002 (0.002)	-0.091 (0.065)	-0.004 (0.004)	-0.006 (0.003)
RR (95% CI)	0.998 (0.993, 1.002)	0.913 (0.804, 1.036)		0.994 (0.989, 0.999)
p value	0.331	0.158	0.313	0.028
Asthma
Overall
β (SE)	+0.003 (0.002)	-0.206 (0.061)	-0.002 (0.003)	+0.000 (0.003)
RR (95% CI)	1.003 (0.998, 1.007)	0.814 (0.722, 0.918)		1.000 (0.995, 1.005)
p value	0.236	<0.001	0.502	0.876
Adults
β (SE)	-0.000 (0.003)	-0.175 (0.072)	+0.002 (0.004)	+0.002 (0.003)
RR (95% CI)	1.000 (0.994, 1.005)	0.840 (0.729, 0.966)		1.002 (0.996, 1.008)
p value	0.922	0.015	0.611	0.552
Children
β (SE)	+0.011 (0.004)	-0.287 (0.118)	-0.015 (0.007)	-0.004 (0.005)
RR (95% CI)	1.011 (1.002, 1.020)	0.751 (0.595, 0.947)		0.996 (0.986, 1.006)
p value	0.015	0.015	0.027	0.424

*The segmented Poisson regression model adjusted for age and sex provides estimates for the trend in ED visits over time prior to the law being passed (β₁), the step change after the law took effect (β₂) and the change in trend after the law took effect (β₃). The sum of β₁ and β₃ corresponds to the trend over time after the law took effect.
Abbreviation: COPD chronic obstructive pulmonary disease.

ISSN: 1471-2466