Re Chalder fatigue scale and the ceiling effect:
But there is a counter argument that people on the ceiling could "improve" without showing a fall in their score, since they are already off the scale.
So people fill in the questionnaire a little 'better.'
The Chalder Fatigue Scale scoring deosn't quite work like that.
It is a bit weird, see below.
"If you have been feeling tired for a long while
, then compare yourself to how
you felt when you were last well. [score each of 11 items]
Less /same/More than usual/Much more than usual [scored 0-3 for Likert]
e.g. Do you have problems with tiredness"
More:
https://studylib.net/doc/11997962/chalder-fatigue-scale
One issue problem is that zero is "less than usual", which would equate to "less than when you last felt well"! So effectively the minimum score is 1, making it an 11 to 33 point scale, a range of 23 points.
The maximum score of 3 is for "much more than usual". This is where the ceiling problem comes in, when many patients would say there tiredness is "way, way more than usual".
Somebody who at the start of the trial might regard themselves as "way, way more tired than usual" but can still only score the maximum 3 points. At the end of it may feel they have improved (whether this is due to response bias or not is irrelevant) and feel that their tiredness is now only "much more than usual". As a result the score for that question remains at 3: this is the ceiling effect of not been able to measure a change. That's the very long explanation of I meant by my rather brief original comment!
The Chalder fatigue scale has many flaws, regardless of the response bias issue. And the ceiling effect is one of those flaws.
I find it difficult to believe that many patients would consider a 3.4 change to be important in trials of the sort assessed in this review. But who knows? It seems no-one bothered to ask us.
This is a really good point. Some studies attempt to "anchor" the claimed "minimal useful difference" or whatever by comparing it to other questionnaires, such as overall change in health (to anchor a change in a pain scale, for instance).
A better way to do that would be to ask patients if the change they report on a fatigue scale corresponds to what they consider a useful change in fatigue (you would need to do this as part of a double-blind study, e.g. for a rheumatoid arthritis drug, to avoid problems of response bias).
That might give a much better measure of what counts as a useful change for a subjective symptom (leaving aside response bias issues).