Statistical analysis

Statistical analysis included one-way analysis of covariance (ANCOVA) to compare bimanual parameters between children with uCP and age- and sex-matched TDC with age as covariate. The parameters were transformed if the Shapiro–Wilk test indicated that the residuals from the ANCOVA were not normally distributed. An overview of the transformations can be found in  Additional file 1. In case of transformation, all results were back-transformed and reported in this study for optimal interpretation [28]. Moreover, when unequal variances were present between groups (Levene’s test, p ≤ 0.05), ANCOVA was performed using robust standard errors [29, 30]. If there was no significant interaction between age and group, only the model with the main effects was retained. When an interaction effect was found between group and age, a moderated regression analysis was performed instead of an ANCOVA [31]. Lastly, to correct for multiple testing, a false discovery rate was implemented with an adjusted p-value of 0.05, indicating that only 5% of significant tests will result in false positives [32, 33]. Effect sizes were calculated using partial eta squared (ηp2) and interpreted as small (0.01–0.059), medium (0.06–0.13), and large (≥ 0.14) [34]. For the second research question, an ANCOVA following the same procedure as described above was used to compare the bimanual parameters between MACS-levels (Levels l–lll) in children with uCP. Finally, the relation between the bimanual, unimanual and task execution parameters was investigated with Pearson (r) and Spearman’s rank correlations (r_s), depending on the data distribution, and interpreted as no or little (< 0.30), low (0.30–0.49), moderate (0.50–0.69), high (0.70–0.89) and very high (≥ 0.90) [35]. Matlab 2021a (Mathworks, Natick, MA) was used for data analysis of the circuit task and SPSS Statistics version 26.0 (IBM, Armonk, New York, USA) was used for all statistical analyses. We further used the PlotsOfData application to visualize the difference in bimanual coordination between children with different MACS-levels. [36]