Table 1. Characteristics of fist-born twins.
| Characteristics | Mean | SD |
|---|---|---|
| N | 637 | — |
| Female(%) | 51.3 | — |
| Baseline age (year) | 10.66 | 2.30 |
| SE at baseline (diopter) | −0.52 | 1.97 |
SE: spherical equivalence, SD: standard deviation.
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