Ires Ghielen

28 Chapter 2 Associations between anxiety, depression, motor dysfunction and autonomic failure in PD Histograms demonstrated that the residuals of both the total BAI score and subscales of the BAI had a positively skewed distribution. Transformation of the data did not improve normality. To maintain interpretability of results, we decided to use the original data for the analyses. Homoscedasticity was confirmed by plotting the regression standardized predicted value against the regression standardized residual. Both the correlations (see Table 2) and the VIF (ranging from 1.005 to 1.610) indicated non-collinearity of the data. Table 2. Matrix of the Pearson’s correlation coefficients (r) for the BAI, BDI, SCOPA-AUT, UPDRS-III and age. BAI BDI SCOPA-AUT UPDRS-III Age BAI 1.000 0.735** 0.616** 0.234** 0.100 BDI 0.735** 1.000 0.535** 0.230** 0.120* SCOPA-AUT 0.616** 0.535** 1.000 0.330** 0.277** UPDRS-III 0.234** 0.230** 0.330** 1.000 0.300** AGE 0.100 0.120* 0.277** 0.300** 1.000 *p-value < 0.05, **p-value < 0.01 (2-tailed). Results of the multiple regression analyses with the BAI total score and subscales of the BAI as dependent variable are presented in Table 3. In this table, the final, adjusted models are displayed, showing the influence of each independent variable on the outcome variable. The unadjusted and adjusted models, including detailed information on confounding, can be found in Supplementary Table S1. The BAI total score was significantly influenced by age and gender: younger patients and females had a higher score on the BAI than older patients and men. The BAI score also increased with a higher score on the BDI and SCOPA-AUT. The UPDRS-III score no longer significantly influenced the BAI score after adjustment for score on the BDI and SCOPA-AUT. All subscales of the BAI were influenced by the BDI score. Moreover, the subscales thermoregulation and hyperventilation were significantly influenced by the SCOPA- AUT, the trembling subscale by the UPDRS-III, and the hypotension subscale by both. The affect subscale was only significantly influenced by the BDI score, and not by the SCOPA-AUT and UPDRS-III. The relationship between the BAI total score and the subscales of the BAI and the BDI, SCOPA-AUT and UPDRS-III were influenced by confounders, as mentioned in the addendum of Supplementary Table