Baseline and follow-up characteristics of the 776 participants by gender
| Variables | Total (N=776) | Boys (n=416) | Girls (n=360) | P value* |
| Mean (SD) | ||||
| Baseline age (years) | 9.64 (1.54) | 9.69 (1.49) | 9.59 (1.59) | 0.375 |
| Average daily outdoor time (hours) | 2.04 (1.18) | 2.06 (1.20) | 2.01 (1.17) | 0.548 |
| Height (cm) | ||||
| Baseline | 143.50 (11.17) | 144.44 (11.40) | 142.40 (10.80) | 0.021 |
| Follow-up | 154.53 (15.61) | 156.63 (14.96) | 151.72 (17.21) | <0.001 |
| Changes | 11.03 (11.55)† | 12.38 (8.16)† | 9.41 (14.44)† | 0.001 |
| AL (mm) | ||||
| Baseline | 24.02 (1.13) | 24.29 (1.10) | 23.71 (1.08) | <0.001 |
| Follow-up | 24.64 (1.20) | 24.91 (1.19) | 24.32 (1.13) | <0.001 |
| Changes | 0.60 (0.33)† | 0.60 (0.33)† | 0.60 (0.34)† | 0.964 |
| SE (D) | ||||
| Baseline | −1.09 (2.00) | −1.17 (1.97) | −0.98 (2.03) | 0.241 |
| Follow-up | −2.04 (2.30) | −2.05 (2.35) | −2.02 (2.25) | 0.880 |
| Changes | −1.06 (0.66)† | −1.05 (0.67)† | −1.08 (0.64)† | 0.563 |
| Estradiol (pg/mL) | ||||
| Baseline | 2.79 (0.96) | 2.70 (1.00) | 2.92 (0.90) | 0.063 |
| Follow-up | 4.44 (2.58) | 4.15 (2.38) | 4.86 (2.79) | 0.040 |
| Changes | 1.71 (2.82)† | 1.56 (2.72)† | 1.96 (2.98)† | 0.363 |
| Testosterone (pg/mL) | ||||
| Baseline | 51.32 (21.86) | 54.34 (24.38) | 47.25 (17.18) | 0.006 |
| Follow-up | 81.69 (34.05) | 93.65 (34.95) | 64.21 (23.69) | <0.001 |
| Changes | 33.77 (30.45)† | 42.68 (30.36)† | 19.48 (24.77)† | <0.001 |
| n (%) | P value‡ | |||
| Myopia§ | ||||
| Baseline | 350 (55.2) | 198 (57.2) | 152 (52.8) | 0.262 |
| Follow-up | 343 (69.9) | 196 (69.3) | 147 (70.7) | 0.736 |
| Changes | 73 (36.1) | 36 (32.7) | 37 (40.2) | 0.270 |
| Menarche/first spermatorrhoea occurrence | ||||
| Baseline | 83 (13.2) | 36 (10.5) | 47 (16.3) | 0.032 |
| Follow-up | 269 (34.7) | 78 (18.8) | 191 (53.2) | <0.001 |
| Changes | 143 (26.2) | 40 (13.1) | 103 (42.9) | <0.001 |
*P value for comparison between boys and girls using a t-test.
†P <0.01 for comparison between baseline and follow-up using paired t-test.
‡P value for comparison between boys and girls using chi-square test.
§A total of 634 subjects at baseline and 491 subjects at 2-year follow-up participated in the cycloplegic refraction.
AL, axial length; SE, spherical equivalent.