Table 5. Sociodemographic and household variables and nutritional status in relation to boys’ lung function by period.

Variables	Period 1						Period 2
	FVC (mL)			FEV1 (mL)			FVC (mL)			FEV1 (mL)
	Mean (SD)	P value		Mean (SD)	P value		Mean (SD)	P value		Mean (SD)	P value
Residential location
Rural	2,727 (632)	<0.001		2,256 (548)	<0.001		2,047 (435)	0.025		1,802 (363)	0.665
Urban	2,468 (566)			2,020 (471)			1,924 (362)			1,802 (312)
ETS
No	2,358 (568)	0.049		1,929 (499)	0.063		2,037 (460)	0.550		1,808 (374)	0.776
Yes	2,632 (609)			2,167 (517)			1,994 (393)			1,800 (332)
Sleeping in own room
Yes	2,904 (696)	<0.001		2,398 (598)	<0.001		2,073 (438)	0.003		1,943 (386)	0.142
No	2,507 (559)			2,060 (476)			1,831 (360)			1,769 (334)
Sleeping in own bed
Yes	2,642 (621)	0.008		2,164 (529)	0.034		2,045 (438)	0.025		1,825 (355)	0.099
No	2,449 (561)			2,038 (490)			1,933 (358)			1,748 (327)
Kitchen
Open	2,541 (586)	0.010		2,092 (498)	0.028		2,002 (406)	0.511		1,780 (338)	0.123
Separated	2,751 (665)			2,257 (577)			2,031 (441)			1,841 (365)
Coal fuel use
No	2,658 (619)	0.329		2,176 (513)	0.414		2,021 (426)	0.085		1,805 (353)	0.333
Yes	2,575 (609)			2,121 (523)			1,824 (216)			1,698 (260)
Ventilation use
No	2,772 (687)	0.047		2,269 (567)	0.106		1,943 (206)	0.756		1,793 (273)	0.983
Yes	2,564 (596)			2,111 (512)			2,014 (421)			1,802 (350)
Paternal occupation
Nonmanual laborer	2,709 (674)	0.049		2,210 (563)	0.083		2,102 (450)	0.052		1,873 (373)	0.028
Manual laborer	2,555 (589)			2,107 (507)			1,985 (405)			1,780 (339)
Maternal occupation
Nonmanual laborer	2,664 (620)	0.136		2,203 (519)	0.066		2,055 (443)	0.256		1,813 (359)	0.491
Manual laborer	2,565 (607)			2,106 (520)			1,996 (408)			1,798 (345)
Paternal education
~Senior high school	2,750 (839)	0.487		2,253 (660)	0.393		2,022 (432)	0.789		1,794 (358)	0.343
Senior high school~	2,578 (592)			2,121 (510)			2,001 (404)			1,812 (338)
Maternal education
~Senior high school	2,779 (768)	0.493		2,276 (587)	0.380		2,023 (443)	0.695		1,813 (368)	0.728
Senior high school~	2,581 (603)			2,123 (518)			2,003 (395)			1,792 (330
Breast feeding
No	2,418 (621)	<0.001		1,985 (501)	0.004		1,973 (374)	0.367		1,789 (343)	0.800
Yes	2,630 (602)			2,164 (521)			2,025 (432)			1,806 (351)
Stunting
No	2,607 (607)	0.002		2,143 (519)	0.005		2,012 (419)	NA		1,802 (349)	NA
Yes	2,056 (483)			1,730 (428)			NA			NA
Obesity
No	2,580 (616)	0.266		2,120 (523)	0.145		1,944 (374)	<0.00		1,754 (322)	<0.001
Overweight	2,803 (513)			2,338 (476)			2,090 (429)			1,854 (353)
Obesity	2,699 (300)			2,297 (368)			2,224 (504)			1,954 (405)

~Senior high school: below senior high school level; senior high school~: with/above senior high school. NA, no data available, which presents no male children in Period 2 were found stunting; FVC, forced vital capacity; FEV₁, forced expiratory volume in the first second; SD, standard deviation.