Dr David Tuller: Dutch CBT Study for Long Covid Proves that Unblinded Studies with Subjective Outcomes Generate Positive Reports


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Trial By Error: Dutch CBT Study for Long Covid Proves that Unblinded Studies with Subjective Outcomes Generate Positive Reports​


6 Comments / By David Tuller / 25 May 2023
By David Tuller, DrPH

Three years ago, I wrote a blog post about a problematic Dutch study that had been funded by a major health agency and was being led by Hans Knoop, a professor of medical psychology at Amsterdam University Medical Centers. The study sought to test whether a course of cognitive behavior therapy starting months after a bout of acute Covid-19—rather than years later— could reduce levels of reported fatigue and prevent it from becoming chronic.
Professor Knoop is a long-time colleague of the authors of the now-discredited PACE trial. In a Lancet commentary accompanying the publication of the PACE results, he and a colleague declared that many patients had met “a strict criterion for recovery”—a ridiculous and untrue claim.

This new study—like so much of the research from Professor Knoop and his colleagues in the world of psychosomatic medicine—was unblinded and relied on subjective, self-reported outcomes. This design is fraught with potential bias. Given the design, the study was destined to produce positive results on these subjective outcomes—and now, not surprisingly, it has, with the results published in the journal Clinical Infectious Diseases.

Also not surprisingly, the results for the one objective outcome included in the protocol—actigraphy to measure levels of physical activity at baseline and right after treatment—were not reported or mentioned in the paper. Professor Knoop has deployed this strategy before—most recently in 2017 when he and colleagues published positive subjective outcomes but failed to report null actometer results in a study of CBT for treating fatigue after Q-fever; these null results were published two years later and ignored. And in a similar fashion a dozen years ago, Professor Knoop and several colleagues buried disappointing actigraphy results from three trials of CBT for ME/CFS.
Twitter threads from @lucibee and @anilvanderzee point out some of the major issues with the new study, called “Efficacy of cognitive behavioral therapy targeting severe fatigue following COVID-19: the results of a randomized controlled trial.” The study was also the subject of a lively discussion on the Science For ME forum. The CBT course, called “Fit After Covid,” included online modules along with in-person or online contact with a therapist.

The study’s 114 participants were all suffering from what was identified as severe fatigue three to 12 months after their acute infections. They were randomized into a group receiving the CBT program and group receiving care as usual (CAU)—a design that undermines the claim in the article title that the study was “controlled.”
Yes, there was a comparison arm. But the mean number of interactions between therapist and patient in the CBT arm was almost 12, and the study did not offer members in the CAU group a parallel amount of time and attention.
If participants know they are receiving an active treatment in a trial—a full course of therapeutic encouragement, for example—and they are told that this treatment has been found to be successful in other circumstances, it stands to reason they would be more likely to report benefits than people who know they did not receive the possibly helpful treatment. The authors mention this imbalance between the groups as a limitation but nonetheless still call the trial “controlled,” even though they are not controlling for this important factor.