There's a lot to say about that
trial by Prins et al. 2001.
1) There was an enormous drop-out rate (28-41%, depending on how you define it). From the 93 who were randomized to CBT, only 55 completed the trial.
2) Objective outcomes such as neuropsychological testing and actigraphy were only reported many years later in separate reviews (you have to look at the references to know it's data from that trial). These did not show a significant difference. Work resumption was reported in the 2001 paper, and there were also no differences between groups.
3) The control group failed, it did worse than the natural course of the illness, so the cost-effectiveness compared CBT to the latter.
4) No follow-up data is reported, which is strange because two people publically stated that such data existed and that these did not show significant results. The first person is Kenneth M Lassesen. He wrote in
a letter to the editor, in 2001:
"After hearing a presentation on Judith Prins and colleagues’ study1 at the American Association for Chronic Fatigue Syndrome (AACFS) International Conference, Seattle, in January, 2001, I find disturbing the lack of full disclosure. At the AACFS, a question was asked about the length of benefit for CBT. The presenter stated that the natural course and CBT groups did not differ significantly 3 years after treatment."
The other person is Elke van Hoof. She wrote in
an Editorial in the Journal of Chronic fatigue syndrome, in 2003:
"Most treatment studies that achieve a 1/3rd improved, a 1/3rd no change and a 1/3rd worsened result are observing an ineffective therapy as the changes appear to be a result of the normal course of the disease process. This is consistent with the report by one of the coresearchers that the effects of CBT were no longer present after 3 years (Bleijenberg G, communication, Fifth International Research, Clinical and Patient Conference)."
5) As noted, there's the issue of selection criteria:
"Patients were eligible for the study if they met the US Centers for Disease Control and Prevention criteria for CFS, with the exception of the criterion requiring four of eight additional symptoms to be present."
Which is weird. This research group used to apply to Oxford definition (but that definition differs from the first criteria of the Fukuda-criteria because fatigue has to be the main symptom). Perhaps they realized the CDC criteria had more prestige so it was better to present the results as such. I don't know.
6) The study was funded by "a grant from the Health Insurance Council (College voor Zorgverzekeringen)."
The results were published in the Lancet (for some reason they seem to like these kinds of flawed CBT-trials). When PACE-defenders say there are many other trials who have found similar results, they are talking about flawed trials like this one.