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. 2025 Aug 6;25:2674. doi: 10.1186/s12889-025-23599-y

Table 4.

Differences in children’s cognitive levels by birth order and gender

1.All sample 2.Male (N = 674) mean (SD) 3.Female (N = 651) mean (SD) 4.Gender differences(Cohen’s d)
(1) Only child (N = 338) 95.90(11.58) 94.7(11.32) 97.36(11.77) 2.66(0.23)**
(2) Have siblings (N = 987) 94.82(10.10) 95.07(10.00) 94.57(10.21) −0.49(0.05)
(3) The eldest of siblings (N = 305) 95.77(9.93) 96.19(9.60) 95.41(10.22) −0.78(−0.08)
(4) The youngest of siblings (N = 607) 94.89(10.20) 94.96(10.13) 94.81(10.30) −0.16(−0.02)
(5) The middle of the siblings (N = 70) 90.07(8.69) 87.07(8.69) 90.79(9.00) 2.97(0.34)
(6) Diff (3)-(1)(Cohen’s d) −0.13(−0.01) 1.5(0.14) −1.95(−0.18) −3.45(−0.32)**
(7) Diff (4)-(1)(Cohen’s d) −1.01(−0.09)_ 0.26(0.03) −2.57(−0.24)** −2.82(−0.26)*
(8) Diff (5)-(1)(Cohen’s d) −5.83(−0.52)*** −6.88(0.62)** −6.57(−0.59)*** 0.31(0.03)

Rows (6)-(8) show the differences between children in multi-child families with different sibling structures and those who are only children. The last column shows the difference between girls and boys

* p value < 0.1 (marginally significant)

**p-value < 0.05

***p value < 0.01