Nonlinearities in theory-of-mind development: New evidence from Dutch and Italian boys and girls

The extent to which Theory of Mind (ToM) performance is influenced by cultural and gender differences remains a subject of debate. A sample of 324 Dutch and 511 Italian children (52% boys; 2.8–11.7 years; 50% boys; 2.6–10.3 years; respectively) was administered the ToM Storybooks. Analysis focused on indicators of nonlinearity: moving standard deviations, moving skewness, and moving rate-of-change. Loess curve smoothing was used and showed local peaks in these nonlinear indicators. A first peak was found around the age of 51 months, a local minimum between 70 and 79 months, and a small peak at 85 months. The first peak was statistically significant in all groups (though timing differed in gender and culture), for two out of three nonlinear indicators phenomena, except for Dutch girls (peak 2 and 3 was significant). These results show a substantially nonlinear development regardless gender and culture, but a different timing in development.