Changes in Stress-Strain Index in School-Aged Children: A 3-Year Longitudinal Study

Table 2

The baseline and follow-up characteristics of the 217 participants.

Parameters	7.0–8.0 years old	8.1–9.0 years old	Z	value
	n = 89	n = 128
AL
Baseline	22.84 (22.41, 23.41)	23 (22.54, 23.52)	−1.312	0.189
Follow-up	23.71 (23.16, 24.59)	23.86 (23.34, 24.5)	−0.614	0.539
Change	0.82 (0.61, 1.24)	0.8 (0.52, 1.16)	−1.259	0.208
SSI
Baseline	0.98 (0.89, 1.08)	1.01 (0.92, 1.11)	−1.252	0.210
Follow-up	0.94 (0.84, 1.01)	0.92 (0.83, 1.01)	−0.504	0.615
Change	−0.08 (−0.17, 0.04)	−0.09 (−0.19, −0.01)	−1.090	0.276
SE
Baseline	0.75 (0.13, 1.13)	1 (0.5, 1.28)	−2.303	0.021
Follow-up	−0.88 (−2.63, 0)	−0.75 (−1.91, 0.25)	−1.467	0.142
Change	−1.63 (−2.63, −0.88)	−1.63 (−2.25, −1)	−0.527	0.598

AL, axial length; SE, spherical equivalent; SSI, stress-strain index. , value for comparison between boys and girls using a Wilcoxon test.