Table 1.

Baseline characteristics of children and adolescents. N and percentage (%) for categorical data and mean and standard deviation for continuous data

	Boys (n = 1032)		Girls (n = 1251)		Total (n = 2283)
Age*, year	13.36	3.11	13.77	3.36	13.58	3.26
Age-group*
7–8	73	7.07	94	7.51	167	7.31
9	97	9.40	126	10.07	223	9.77
10	115	11.14	128	10.23	243	10.64
11	111	10.76	116	9.27	227	9.94
12	119	11.53	104	8.31	223	9.77
13	103	9.98	80	6.39	183	8.02
14	78	7.56	62	4.96	140	6.13
15	74	7.17	98	7.83	172	7.53
16	82	7.95	140	11.19	222	9.72
17	78	7.56	151	12.07	229	10.03
18	102	9.88	152	12.15	254	11.13
Residential areas*
Urban	514	49.81	702	56.12	1216	53.26
Rural	516	50.00	549	43.88	1065	46.65
Study sites*
Shaanxi Province	333	32.27	309	24.70	642	28.12
Hainan Province	699	67.73	942	75.30	1641	71.88
Stature*, cm	152.55	16.13	148.67	12.19	150.43	14.24
Weight*, kg	42.11	13.87	39.2	10.63	40.51	12.28
BMI, kg/m2	17.58	3.16	17.37	2.78	17.47	2.96
Vertical jump*, cm	22.93	6.80	18.11	4.08	20.18	5.92
Hand grip strength*, kg	22.30	11.55	16.61	6.87	19.17	9.69
Sit-and-reach*, cm	3.58	7.31	7.33	7.18	5.72	7.47

^*p < 0.05 for the comparison between boys and girls