Table 4.

Mean outdoor airflow stratified by round.

Variable	Mean (SD) outdoor airflow (m3/hour)			P-value for paired T-test
	Overall	Heating season	Cooling season
Overall	820 (1600)	560 (420)	1100 (2300)	0.048
Median household income ($)
20K- ≤40K	830 (1200)	600 (390)	1120 (1800)	0.495
>40K- ≤ 80K	1200 (2600)	690 (560)	2000 (3800)	0.035
>80K	390 (250)	370 (210)	420 (300)	0.616
HVAC
Yes	940 (2200)	570 (520)	1400 (3200)	0.027
No	740 (1100)	550 (360)	1000 (1500)	0.557
Classrooms with no windows or broken windows
Yes	660 (580)	560 (500)	800 (700)	0.101
No	840 (1700)	560 (420)	1200 (2500)	0.836