The association between SE and AL with parental refractive status was estimated using linear mixed-effect models (
Table 2). Parental education level and maximum family income were excluded from the model due to their insignificant correlation with SE (paternal education level,
P = 0.39; maternal education level,
P = 0.22; maximum income,
P = 0.80) and AL (paternal education level;
P = 0.54; maternal education level;
P = 0.67; maximum income;
P = 0.68) in the multiple regression. Only sex was adjusted for in the final mixed model. The negative slope for age (−0.63,
P < 0.001) and the positive slope for age
2 (0.02,
P < 0.001) suggest that the decline in SE decelerated as participants got older. The parental effect was strongly significant, with children having parental myopia being more myopic on average at the age of 7 (
P < 0.001). The coefficients for the interaction between parental refractive status and age was significant, indicating that the rate of decline in SE with age differed across different groups. The more negative coefficient suggested that the rate of myopia progression was on average faster for children with parental myopia (non–mod group, β = −0.03,
P = 0.01; non–high group, β = −0.1,
P < 0.001; mod–mod group, β = −0.1,
P < 0.001; mod–high/high–high group, β = −0.15,
P < 0.001). Similarly, AL elongation also showed a curved pattern that the increase in AL decelerated with age. At the age of 7, children with parental myopia showed a longer AL compared to children without (all
P < 0.05). Axial elongation was on average faster for children with parental myopia (non–high group, β = 0.05,
P < 0.001; mod–mod group, β = 0.03,
P < 0.001; mod–high/high–high group, β = 0.05,
P < 0.001), except for children in the non–mod group (β = 0.01,
P = 0.118).