Table 5.

Percentage change in same-day (lag 0) outpatient visits for psoriasis associated with a 10-μg/m³ increase in airborne concentrations of fine particulate matter using various degrees of freedom (df) for calendar time, temperature, and relative humidity.

Variable	df	Percentage change	95% confidence interval	P- value
Calendar time	6	0.29	0.26–0.32	<0.001
	7*	0.24	0.21–0.27	<0.001
	8	0.24	0.20–0.27	<0.001
	9	0.17	0.14–0.20	<0.001
Temperature	5	0.29	0.26–0.32	<0.001
	6*	0.33	0.30–0.36	<0.001
	7	0.31	0.28–0.34	<0.001
	8	0.29	0.26–0.32	<0.001
Relative humidity	3*	0.29	0.26–0.32	<0.001
	4	0.29	0.26–0.32	<0.001
	5	0.29	0.26–0.32	<0.001
	6	0.29	0.26–0.32	<0.001

^*The df value used in this study model.