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Table 4 Linear mixed model analysis results for the FSS-9, FSS-3 and the Visual analog Fatigue Scale (VAFS)

From: Validation of a three-item Fatigue Severity Scale for patients with substance use disorder: a cohort study from Norway for the period 2016–2020

  Fixed effects Random effects ICC
Baseline Change Residual Intercept Slope Covi,s
I P S P σ2e P σ2i P σ2s P σ2is P
FSS-9a 4.76 *** 0.01   1.46 *** 1.61 *** 0.00   − 0.02   0.52
FSS-3b 4.64 *** 0.00   2.07 *** 1.64 *** 0.00   − 0.01   0.44
Item 1 5.35 *** 0.02 * 2.52   1.53 *** 0.00   − 0.04   0.38
Item 2 4.71 *** 0.03 ** 2.95 *** 1.41 *** 0.00   − 0.03   0.32
Item 3 4.51 *** 0.03 ** 2.40 *** 2.13 *** 0.00   − 0.02   0.47
Item 4 4.90 *** 0.03 ** 3.43 *** 0.73 * 0.00   − 0.04   0.18
Item 5 sv 4.38 *** 0.02   2.99 *** 1.84 *** 0.00   − 0.02   0.38
Item 6 sv 4.57 *** − 0.01   3.18 *** 1.60 *** 0.00   − 0.01   0.34
Item 7 sv 4.97 *** 0.00   2.92 *** 1.62 *** 0.00   − 0.02   0.36
Item 8 4.60 *** 0.02   2.92 *** 2.50 *** 0.00   − 0.02   0.46
Item 9 4.82 *** − 0.01   2.90 *** 1.90 *** 0.00   − 0.00   0.40
VAFS 5.14 *** 0.02 * 4.73 *** 2.27 *** 0.00   − 0.02   0.33
  1. The table shows the linear mixed model analyses, including the fixed effects, the random effects, and the ICC of the FSS-3, FSS-9, VAFS, and the single items of the FSS-9. The random effects show the residual, the slope, and the covariance between the intercept and slope
  2. Covi,s, Covariance between intercept and slope; ICC: Intraclass Correlation Coefficient of between on total variance; I: Intercept (baseline); S: Slope (change); σ2: variance (residual, intercept and slope); σ2i,s: Covariance between intercept and slope
  3. *P < 0.05; **P < 0.01; ***P < 0.001
  4. aFSS-9: Nine-item Fatigue Severity Scale
  5. bFSS-3: Three-item Fatigue Severity Scale
  6. svItems included in the FSS-3