By ME/CFS skeptic.
Problems with the amended version (Version published: 02 October 2019) part I.
I appreciate the efforts made by Cochrane and the authors to correct some of the errors in the previous version of this review. There are however some major problems that remain and significantly impact the results and conclusion. I hope to clarify these in my comments below. I have divided these into two submissions because the text is rather long. All my comments concern the main comparison of graded exercise therapy (GET) versus a passive control condition (treatment as usual or relaxation/flexibility therapy). This is part I.
1) ‘Long-term’ follow-up results downplayed
The review highlights assessments made directly after treatment ended and downplays assessments made several months later even though the latter formed the primary outcome for the trials that provide most of the data.
The authors’ conclusions in the abstract for example states: “Exercise therapy probably has a positive effect on fatigue in adults with CFS compared to usual care or passive therapies.” At follow-up, however, the difference in fatigue scores between the exercise- and passive control groups were no longer statistically significant (Analysis 1.2). The three largest trials which provide most of the data in this Cochrane review (PACE, FINE, and Powell et al., 2001) defined their primary outcome at this follow-up assessment 52 to 70 weeks post-randomization. Their intent was likely to reduce bias as one of these trials, the FINE trial, noted that “assessment at week 70 is required because short-term assessments of outcome in a chronic health condition such as CFS/ME can be misleading.” Using interim assessments made directly after treatment ended, to claim that “exercise therapy probably has a positive effect on fatigue” seems unwarranted as the majority (75%) of the data for this comparison comes from trials that defined their primary outcome several months later. At that time point, the pooled between-group differences were no longer statistically significant. This is true for other outcomes as well, such as physical functioning.
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