Table 4.

Unadjusted and adjusted (least squares) means of indoor PM₁₀ by school or classroom features.

Explanatory variables	PAS		Gravimetry
	Unadjusted	Adjusteda	Unadjusted	Adjusteda
Continuous variable (exponentiated coefficient corresponding to IQR change)b
PAS outdoor PM10, IQR	1.06	1.29**	0.99	1.17**
Classroom density, #/m2, IQR	1.08*	1.08*	1.36**	1.19**
Air cleaner operation
(Ref.) No	67.6	87.5	41.9	30.3
Yes	39.8**	57.6**	33.3*	28.7
School region
(Ref.) North Metro	38.0	49.0	30.1	24.1
Middle	67.7**	80.0**	59.5**	38.0**
South	48.1		46.6**
Island	52.6**	91.5**	32.6	28.0
School area
(Ref.) Commercial	45.2	83.8	34.1	37.5
Residential	44.7	60.2**	36.6	23.2**
Grade
(Ref.) 1	59.9	65.9	32.6	–
2	33.4**	46.9*	27.8	–
3	41.1**	67.8	28.6	–
4	48.7	66.6	41.2	–
5	46.3	77.4	42.0	–
6	77.5	119.0	46.9	–
Surrounding school are
(Ref.) None	41.1	–	34.1	33.2
Ocean	50.7	–	40.0	31.1
Hills with trees	47.3	–	38.8	41.3
Farm	43.0	–	22.8	17.8**
Traffic volume near school
(Ref.) Low	53.3	–	28.8	39.9
Moderate	52.5	–	51.6
High	46.5	–	37.4	33.3
Very high	37.9	–	29.7	19.6**
Windows ever opened during the measurement day
(Ref.) No	46.4	–	38.3	32.4
Yes	36.1	–	25.5**	26.9
Cleaning method
(Ref) Dry	42.5	–	33.4	–
Wet	47.8	–	37.8	–
Construction near school
(Ref.) No	44.7	–	34.0	37.7
Yes	45.7	–	45.8**	23.1
Wearing indoor shoes or bare foot
(Ref) Bare foot	45.3	81.6	35.5	–
Indoor shoes on	44.8	61.8	35.8	–

^aR² (adjusted R²) are 0.39 (0.32) for the final model of PAS (portable aerosol spectrometer) measurements and 0.44 (0.36) for the gravimetric measurements.

^beffects of continuous variables were estimated from coefficients based on IQR (interquartile range) changes in outdoor PM₁₀ concentration (25.6 μg/m³) or classroom occupant density (0.05).

P-values:

^*:0.05–1;

^**:< 0.05.