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Table 6 Psychometric Testing of Final Questionnaire (Reliability, Construct Validity, Responsiveness)

From: Multidimensional daily diary of fatigue-fibromyalgia-17 items (MDF-fibro-17): part 2 psychometric evaluation in fibromyalgia patients

Parameter Threshold for Acceptability MDF-Fibro-17
Total Global Fatigue Experience Cognitive Fatigue Physical Fatigue Motivation Impact on function
Reliability [18, 24]
 • Cronbach’s Alpha ≥0.8 0.99 0.98 0.99 0.94 0.98 0.98
 • Test-retest (ICC) Baseline vs. Week 1/Week 5 versus Week 6 ≥0.7 0.76/0.92 0.71/0.90 0.82/0.94 0.73/0.91 0.75/0.91 0.76/0.92
Construct Validity
 • Convergent Validity at Baseline/End of Active Treatment >0.4       
  o GFI   0.73/0.80 0.75/0.84 0.62/0.69 0.64/0.75 0.73/0.77 0.72/0.76
  o SF-36 VT   0.52/0.66 0.52/0.68 0.43/0.57 0.46/0.60 0.53/0.65 0.50/0.62
  o FIQ Total   0.71/0.80 0.69/0.81 0.59/0.69 0.67/0.76 0.68/0.77 0.70/0.76
  o SF-36 PF   0.42/0.40 0.42/0.39 0.31/0.34 0.43/0.38 0.41/0.39 0.44/0.40
  o SF-36 PCS   0.41/0.50 0.41/0.50 0.28/0.40 0.43/0.50 0.41/0.49 0.43/0.49
 • Divergent validity at Baseline/End of Active Treatment < Convergent       
  o Mood   0.36/0.52 0.29/0.47 0.36/0.53 0.32/0.41 0.34/0.53 0.34/0.52
  o Cognitive function   0.06/0.47 0.04/0.39 0.07/0.54 0.08/0.36 0.03/0.48 0.13/0.47
  o SF-36 other scales   0.27/0.66 0.26/0.66 0.26/0.56 0.27/0.65 0.26/0.59 0.26/0.63
  o Sexual Function   0.18/0.21 0.15/0.17 0.18/0.23 0.14/0.17 0.19/0.22 0.19/0.21
 • Known-groups Validity p < 0.05 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
Responsiveness and Effect Size
 • Change from Baseline to End of Active Treatment p < 0.05 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
 • Effect Size 0.8 and above (Large) 0.91 0.95 0.69 0.94 0.88 0.85
  1. Correlations with other measurements were collected as part of the Phase 2 study. The results are available upon request
  2. FIQ Fibromyalgia Impact Questionnaire, GFI Global Fatigue Index, from the MAF, ICC intraclass correlation coefficient, MDF-Fibro-17 Multidimensional Daily Diary of Fatigue-Fibromyalgia-17, SF-36 36-Item Short Form Health Survey, PCS SF-36 Physical Composite Score, PF physical functioning, VT SF-36 Vitality subscale