Fig. 1

Longitudinal confirmatory factor analysis of the FSS-3 in patients with substance use disorders. FSS-3: Three-item Fatigue Severity Scale. The longitudinal factor analysis structure is shown with the upper circles representing factor 1 and the factor loadings between factor 1 and three separate question items at two different time points (baseline and second health assessment) for the three-item Fatigue Severity Scale [26]. The arrows at the bottom represent the residuals and alfa (α) values for each question item’s standardised mean values. The arrow between the circles represents the correlation (0.52) between the confirmatory factor analyses. The values of 1.86 and 1.78 on the left side of the circles represent the latent variables’ variance