highly significantp < 0.001
Specifically, differences were highly significant for grade (χ 2 = 454.81, p < 0.001) and gender (χ 2 = 378.18, p < 0.001), and significant for only-child status (χ 2 = 6.86, p < 0.05) and place of origin (χ 2 = 8.66, p < 0.05), as shown in Table 5 .