Measuring improvement and deterioration in myalgic encephalomyelitis/ chronic fatigue syndrome: the pitfalls of the Chalder Fatigue Questionnaire, by Karen D Kirke in Journal of the Royal Society of Medicine Vol 114, Issue 2, 2021 December 15, 2020 [DOI: 10.1177/0141076820977843]
Adamson et al. considered a 2-point decrease in Chalder Fatigue Questionnaire score to indicate improvement in fatigue and a 2-point increase in Chalder Fatigue Questionnaire score to indicate deterioration in fatigue.1 While intuitively appealing, data exist that suggest a more complex relationship between changes in Chalder Fatigue Questionnaire
scores and clinical change.
Collin and Crawley studied treatment outcomes at 11 specialist myalgic encephalomyelitis/ chronic fatigue syndrome clinics in England.2 The authors tabulated mean change in Chalder Fatigue Questionnaire score at one year against Clinical Global Impression scores (see additional file 1, table S3). A 2-point decrease in Chalder Fatigue Questionnaire score was reported patients who deemed their health as follows: ‘no change’, ‘a little worse’, ‘much worse’ and ‘very much worse’.
The mean changes in Chalder Fatigue Questionnaire score in those categories were similar, with overlapping 95% confidence intervals within the range [4.77, 2.29]. This suggests that a 2-point decrease in Chalder Fatigue Questionnaire score indicates deterioration or no change in the health of a person with myalgic encephalomyelitis/ chronic fatigue syndrome, not improvement.
Adamson et al. report a mean change in Chalder Fatigue Questionnaire score of 6.52, corresponding to the ‘a little better’ category in Collin and Crawley’s data. For comparison, the mean change of those ‘much better’ was an 11-point decrease in Chalder Fatigue Questionnaire score, and ‘very much better’ was a 14.9-point decrease.
Studies using the Chalder Fatigue Questionnaire as a primary outcome measure may miss or underestimate deterioration, because the Chalder Fatigue Questionnaire obscures it. Studies may overestimate improvement if a 2-point decrease on the Chalder Fatigue Questionnaire is used, when a 10-point decrease may be a more appropriate lower bound.
Anchoring one subjective measure to another can hint at cut-offs for clinically important differences, but the use of more objective outcome measures such as actigraphy would be preferable. The unpopularity of such measures among myalgic encephalomyelitis/ chronic fatigue syndrome researchers may be linked with the stubborn refusal of more objective outcome measures to budge with current specialist treatment.3
