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Table 1 Canonical loadings for the fatigue (criterion) and quality of life (predictor) in the Parkinson group

From: The dimensionality of fatigue in Parkinson’s disease

Variables Mean (SD) Range Loadings
Predictor variables (quality of life)
 1. PD Quality of Life Questionnaire Summary Index, PDQ-39SI 27 (20) 4–65 0.82
 2. Non-Motor Symptoms Questionnaire, NMS-Q 12 (6) 1–21 0.73
 3. Hospital Anxiety and Depression Scale, HADS 12 (7) 3–24 0.71
 4. Non-Motor Symptoms Scale, NMSS 66 (44) 5–190 0.67
 5. Unified Parkinson’s Disease Rating Scale Total, UPDRS 43 (14) 20–73 0.66
 6. Duration of disease (years) 8 (5) 1–22 0.46
 7. Epworth Sleepiness Scale, ESS 8 (4) 1–15 0.40
 8. Age at diagnosis (years) 63 (9) 45–79 0.38
 9. Body mass index, BMI 27 (7) 17–54 − 0.18
 10. Life orientation test, LOT-R 17 (5) 5–24 − 0.40
 11. Montreal Cognitive Assessment, MoCA 26 (4) 15–30 − 0.52
 12. PD sleep Scale 100 (26) 42–144 − 0.53
 13. EPIC Physical Activity Questionnaire, ePAQ 72 (68) 8–318 − 0.43
Criterion variables (Fatigue)
 1. Fatigue Severity Scale, FSS 38 (15) 11–60 0.86
 2. Functional Assessment of Chronic Illness Therapy Fatigue Scale, FACIT-F 32 (12) 14–50 − 0.83
 3. Parkinson Fatigue Scale, PFS 50 (17) 17–77 0.80
 4. Visual Analog Fatigue Scale, VAFS 6 (2) 2–10 − 0.69
  1. All quality of life variables except body mass index reliably predicted perception of fatigue in Parkinson’s disease. The PDQ-39SI produced the strongest prediction