Fig. 2

Sex-by-diagnosis interaction: local gyrification. a Whole-brain analyses (p < 0.01, corrected). In this vmPFC/OFC cluster, we found a significant sex-by-diagnosis interaction, males with ASD show a selective reduction in gyrification as compared to all three other groups. When the smaller brain size of females is not taken into account (upper panel), TD females typically show reduced gyrification. This is however not the case within the ASD group, where even raw lGI values tend to be higher in females than males with ASD. For the post-hoc two-by-two analyses, the following p values are depicted: *p < 0.05, **p < 0.01, ***p < 0.001. b Bootstrapping analyses. The likelihood to observe a significant sex-by-diagnosis interaction in the vmPFC/OFC cluster was tested using a similar bootstrap procedure as for the main effect of sex. Again, the pattern of a decrease in the likelihood to observe any significant effect as the sample size decreases suggests that previous studies of sex differences in ASD were likely underpowered to estimate robust and reproducible effects. c Power analyses. Plot depicting the relationship between statistical power and sample size, computed a posteriori based on the effect sizes obtain in the full dataset