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

ABSTRACT

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.

KEYWORDS:

• ToM Storybooks
• cross-sectional
• loess curve smoothing
• culture
• gender

Acknowledgments

The authors thank the children and families who participated in the studies and the kindergartens and schools that took part in the project.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available on request from the corresponding author, DB. The data are not publicly available due to their containing information that could compromise the privacy of research participants.

Supplementary material

The Supplementary material includes (1) an explanation of the Monte Carlo methods used in order to test hypotheses about the probability of the observed nonlinear phenomena if the null hypotheses (of smooth and monotonic change) were true, and (2) figures of all the nonlinear indicators discussed in the article for the total group and the various subgroups (boys, girls, Italy, Netherlands), including tables specifying p-values and confidence intervals for these indicators.