3.1.4. Convergent validity
Phase 5 took place in January–May 2013. 605 people
were sent the questionnaire, 465 responded (77%). The
association between the IBD-F questionnaire Sections 1 and 2
total score and the other fatigue questionnaires was
examined using Pearson correlation. The IBD-F correlation
coefficient with the MAF was 0.73 (Section 1) and 0.78
(p b 0.001) (Section 2) and with the 5 subscales of the MFI
ranged between 0.47 and 0.65 (all p b 0.001), indicating
moderate correlation with established generic fatigue
scales.
3.1.5. Internal consistency
Internal consistency of the IBD-F and the other questionnaires
was calculated using the Cronbach's alpha value:
for Section 1 it was 0.91; for Section 2 it was 0.98. This
compares favourably with the other fatigue scores: the MAF
Cronbach's alpha was 0.87 and for the 5 scales of the MFI it
ranged from 0.69 to 0.84.