Non-linear regression trees
In addition to linear relations, we also investigated non-linear relationships between measures of inhibitory performance and questionnaires with regression trees. To test the influence of BIS-11 and OCI-R scores, each model was tested via nested cross-validation and on a test set of participants from a different sample. Regression trees from nested cross-validation were also tested in permutation models with shuffled dependent variables to assess their superiority over a random model. Model accuracy is reported via root mean squared error. As is evident from Table 5, the models differ only marginally from one another in terms of accuracy. While the regression tree seems to explain IES better than the linear model on the test set, this does not hold true for our sample data in nested cross-validation. Therefore, non-linear associations between impulsivity and compulsivity with inhibitory performance were not observed.