Fig. 2

Trajectory of child behavior problems with respect to the number of children. a Total difficulty, mean SDQ scores of the only-child in three periods: 10.20, 10.08, 10.17; SDQ scores of non-only child: 10.14, 9.71, 9.44. b Emotional problem, SDQ scores of the only-child: 1.97, 2.05, 1.92; SDQ scores of non-only child: 1.80, 1.76, 1.89. c Externalizing problem, SDQ scores of the only-child: 5.99, 5.94, 5.83; SDQ scores of non-only child: 5.78, 5.77, 5.75. d Social communication problem, SDQ scores of the only-child: 5.25, 4.97, 5.05; SDQ scores of non-only child: 5.35, 5.18, 5.14