4.4.2. Statistical Tests

Normality of distributions as well as linearity and homoscedasticity of data were tested visually (using histograms, normal Q-Q Plots, etc.,) and mathematically using Shapiro–Wilk and Levene’s tests [25,26].

Reliability of the ACSS and its domains was assessed via internal consistency of the items and represented using Cronbach’s coefficient alpha and the coefficient of split-half reliability [27].

Discriminative ability was assessed by comparing the scores of the respective item scores and total domain scores between patients and controls at the diagnostic baseline visit. Responsiveness of the ACSS domains was measured by comparing patients’ total scores on different domains of the ACSS at baseline and follow-up visits and the changes in scores of the ‘dynamics’ domain at various follow-up visits.

Diagnostic abilities of the domains and items of the ACSS were assessed by the measurement of sensitivity, specificity, positive and negative predictive values, diagnostic odds ratio (DOR), Youden’s index and ROC-curve analyses.

Numerical values were presented by the values of measures of central tendency (e.g., mean, median), distribution and dispersion (e.g., standard deviation, 95% confidence intervals, interquartile range). A comparative analysis of the independent continuous variables was performed using a two-sided independent sample t-test and paired t-test with the Welch correction in cases of inequality of variances [28]. Categorical variables were presented in proportions and compared with McNemar’s test [29].

Comparisons of ordinal and interval variables, as well as values of matched groups (e.g., total scores of patients on ACSS domains at baseline and follow-up visits), were performed using the Wilcoxon signed-rank test [30]. The strength of associations was assessed using Pearson’s product-moment correlation coefficient for numerical and interval variables [31]. Statistical significance was set at 0.05.

R v.3.5.2 with in-built and additional packages was used for the analysis and graphical representation of the results [32,33,34,35,36].