. 2017 Nov 27;12(11):e0188678. doi: 10.1371/journal.pone.0188678

Table 1. Characteristic data of the subjects.

	Stage one				Stage two
	ADHD	Control	Statistics	P value	ADHD	Control	Statistics	P value
	(256)	(372)	(χ² or t)	P value	(328)	(431)	(χ² or t)	P value
Age(mean±SD)^a	8.20±1.53	8.34±1.72	1.048	0.148	8.51±1.78	8.60±2.10	0.624	0.266
Gender(boys: girls)			0.324	0.570			3.157	0.076
Boys	201	299			263	322
girls	55	73			65	109
IQ score(mean±SD) ^a	96.57±12.35	97.52±11.25	1.000	0.159	89.33±11.21	90.49±11.60	1.385	0.083
Maternal stress pregnancy
No	149	256	7.460	0.006	251	349	4.700	0.030
Yes	107	116			77	72
Maternal smoking
No	241	356	0.785	0.376	314	422	3.013	0.083
Yes	15	16			14	9
Maternal alcohol
No	239	359	3.299	0.069	311	415	0.969	0.325
Yes	17	13			17	16
Parental marital status
Couple	229	350	4.525	0.033	314	416	3.013	0.083
Divorced	27	22			14	12
Preterm birth
≥37 weeks	214	330	3.425	0.064	298	380	2.870	0.090
<37 weeks	42	42			30	51
Low birth weight
<2.5kg	34	28	5.643	0.018	35	29	3.749	0.053
≥2.5 kg	222	344			293	402
Blood lead level^b
Low	117	202	6.783	0.009	152	228	3.205	0.073
High	149	169			176	203
Subtype
Inattentive(ADHD-I)	102(40%)				138(42%)
Hyperactive/impulsive(ADHD-HI)	64(25%)				79(24%)
Combined(ADHD-C)	90(35%)				111(34%)
PSQ score(mean±SD) ^a
Impulsive-hyperactive score	1.36±1.20	1.27±1.05	-0.995	0.160	1.52±0.84	1.45±0.82	-1.153	0.125
Hyperactive score	1.32±0.41	1.24±0.42	-2.368	0.009	1.58±0.92	1.36±0.96	-3.184	0.001
Total score	38.98±17.56	37.86±11.15	-0.977	0.164	40.21±18.02	38.97±16.59	-0.983	0.163

^a mean ± SD, by independent t-test;

^b Stage one: low <Median 54.50ug/l, High≥54.50 ug/l; Stage two: low <Median 55.05ug/l, High≥55.05ug/l; Bold values indicated P< 0.05.