On 2014 Feb 20, Tom Kindlon commented:
Further evidence showing why objective measures are preferable in CFS trials particularly where cognitions could be changed following the intervention
(This was originally posted as an e-letter here in 2009: http://www.biomedcentral.com/1471-2377/7/6/comments#333618. However, many people will not read the paper on PubMed Central and so not see it there)
Since writing my previous posts, further data on the subject has come to my attention.
Friedberg and Sohl [1] have just published the results of a study on an intervention involving Cognitive Behavior Therapy (CBT) which included encouraging patients for going for longer walks. It found that on the SF-36 Physical Functioning (PF) scale, patients improved from a pre-treatment mean (SD) of 49.44 (25.19) to 58.18 (26.48) post-treatment, equivalent to a Cohen's d value of 0.35. On the Fatigue Severity Scale (FSS), the improvement as measured by the cohen's d value was even great (0.78) from an initial pre-treatment mean (SD) of 5.93 (0.93) to a 5.20 (0.95) post-treatment.
However on actigraphy there was actually a numerical decrease from a pre-treatment mean (SD) of 224696.90 (158389.64) to 203916.67 (122585.92) post-treatment (cohen's d: -0.13). So just because patients report lower fatigue and better scores on the SF-36 PF scale, doesn't mean they're doing more, which is what GET and CBT based on GET claim to bring about. These results seem particularly pertinent for this study given the primary outcome measures are the SF-36 PF scale and a fatigue scale.
Further reading show that another study[2], published over a decade ago, showed the problem of using self-report data in CFS patients. The authors' rationale for the study was: "It is not clear whether subjective accounts of physical activity level adequately reflect the actual level of physical activity. Therefore the primary aims of the present study were to assess actual activity level in patients with CFS to validate claims of lower levels of physical activity and to validate the reported relationship between fatigue and activity level that was found on self-report questionnaires. In addition, we evaluated whether physical activity level adequately can be assessed by self-report measures. An Accelerometer was used as a reference for actual level of physical activity.". The authors reported on the correlations on 7 outcome measures in relation to the actometer readings: "none of the self-report questionnaires had strong correlations with the Actometer. Thus, self-report questionnaires are no perfect parallel tests for the Actometer."
Prof. White seems to be aware of the findings of this study as he has been co-authored at least two papers [3,4] which quoted the findings. One of the times this paper was referenced even shows the problem I'm highlighting e.g. "support for this explanation comes from investigations that have described discrepancies between subjectively reported impairments and objective measures of activity" [4].
The authors of the 1997 study[2] pointed out that "The subjective instruments do not measure actual behaviour. Responses on these instruments appear to be an expression of the patients' views about activity and may be biased by cognitions concerning illness and disability." This was re-iterated in another paper[5]: "In earlier studies of our research group, actual motor activity has been recorded with an ankle-worn motion-sensing device (actometer) in conjunction with self-report measures of physical activity. The data of these studies suggest that self-report measures of activity reflect the patients' view about their physical activity and may have been biased by cognitions concerning illness and disability."
A corollary of the last statement is that reports of improvement in self-report measures in interventions which change "cognitions concerning illness and disability" may not be reliable. "Improvements" in self-report measures may simply show that patients have changed their cognitions with regard to how they view their illness, disability, symptoms, etc rather than actually representing improvements in activity levels and functional capacity.
Thus, I would suggest that actometers should be used whenever possible in CFS trials where one is investigating whether an intervention has brought about increased activity.
It is also interesting to note that in the large Van der Werf (2000) study[5], which involved 277 CFS patients (and 47 healthy controls), the authors divided the patients up "pervasively passive" (representing 24% of the patients), "moderately active" and "pervasively active". They found that "levels of daily experienced fatigue and psychological distress were equal for the three types of activity patterns". So one can't necessarily tell how active a patient is from the fatigue levels they report.
Incidentally they also "there were no significant group, gender or interaction effects for the number of absolute large or relatively large day-to-day fluctuations (Table 2 and Table 3)." "The day-to-day fluctuation measures were based on somewhat arbitrary criteria (1 S.D. and 33% activity change). However, when we post hoc tested alternative criteria (50% or 66% activity change), again no significant group differences between controls and CFS patients emerged." Part of the rationale of many behavioural interventions in CFS patients is said to be to reduce "boom and bust" (sample reference,[6]). However, it may be the case that the frequency of this activity pattern in CFS has been exaggerated.
References:
[1] Friedberg F, Sohl S. Cognitive-behavior therapy in chronic fatigue syndrome: is improvement related to increased physical activity? J Clin Psychol. 2009 Feb 11.
[2] Vercoulen JH, Bazelmans E, Swanink CM, Fennis JF, Galama JM, Jongen PJ, Hommes O, Van der Meer JW, Bleijenberg G. Physical activity in chronic fatigue syndrome: assessment and its role in fatigue. J Psychiatr Res. 1997 Nov-Dec;31(6):661-73.
[3] Fulcher KY, White PD. Strength and physiological response to exercise in patients with chronic fatigue syndrome. J Neurol Neurosurg Psychiatry. 2000 September; 69(3): 302–307.
[4] Smith WR, White PD, Buchwald D. A case control study of premorbid and currently reported physical activity levels in chronic fatigue syndrome. BMC Psychiatry. 2006 Nov 13;6:53.
[5] van der Werf SP, Prins JB, Vercoulen JH, van der Meer JW, Bleijenberg G. Identifying physical activity patterns in chronic fatigue syndrome using actigraphic assessment. J Psychosom Res. 2000 Nov;49(5):373-9.
[6] Deary V, Chalder T: Chapter 11, "Conceptualisation in Chronic Fatigue Syndrome" in Formulation and Treatment in Clinical Health Psychology Edited by Ana V. Nikcevic, Andrzej R. Kuczmierczyk, Michael Bruch
Competing interests
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