Table 4

Correlation analysis of indoor PM_2.5 (fine particles 2.5 μm in diameter and smaller) level with outdoor PM_2.5 level, ASD and OD

	Spearman correlation		Partial correlation analysis
	rho	p Value	rho	p Value	Control variables
Outdoor PM_2.5 level	0.58	<0.001	0.37	<0.001	ASD, OD
ASD	0.52	<0.001	0.34	<0.001	Outdoor PM_2.5 level, OD
OD	0.33	<0.001	−0.05	0.352	Outdoor PM_2.5 level, ASD

ASD, active smoker density: number of smokers per 100 m³; OD, occupant density: number of occupants per 100 m³.