Table 4.

Baseline characteristics of participants exposed to quartile (Q1-Q4) daily average concentrations of methane (CH₄)

Variables		CH4 N = 246,844
		Q1 N = 57,832		Q2 N = 62,400		Q3 N = 64,035		Q4 N = 62,577		p-value
		n	%	n	%	N	%	n	%
Age	mean, SDa	5.72	2.61	5.68	2.84	6.30	3.19	8.25	4.03	< 0.001
Boys		30,067	52.0	32,576	52.2	32,959	51.5	31,654	50.6	< 0.001
Monthly income (NTD)b										< 0.001
	<  15,000	50,495	87.3	55,406	88.8	54,061	84.4	45,909	73.4
	15,000 − 19,999	6026	10.4	5210	8.35	7732	12.1	11,903	19.0
	≥ 20,000	1311	2.27	1784	2.86	2242	3.50	4765	7.61
Urbanization levelc										< 0.001
	1 (highest)	17,455	30.2	19,681	31.5	23,868	37.3	20,823	33.3
	2	14,939	25.8	22,318	35.8	22,219	34.7	19,709	31.5
	3	14,376	24.9	11,388	18.3	10,443	16.3	10,806	17.3
	4 (lowest)	11,062	19.1	9013	14.4	7505	11.7	11,239	18.0
Outcome
Atopic dermatitis		482	0.83	921	1.48	1713	2.68	4188	6.69	< 0.001

Chi-square test; ^aOne-way ANOVA; SD standard deviation

^bMonthly income: New Taiwan Dollar (NTD), 1 NTD is equal to 0.03 USD

^cUrbanization level: The urbanization level was categorized by the population density of the residential area into 4 levels, with level 1 as the most urbanized and level 4 as the least urbanized