Studies like these could not be considered under EBM methodology. They are not the highest "standard" of evidence, and so were excluded. There are several problems with EBM "standards". EBM i s theoretically sound, but its application is frequently severely flawed.
EBP or evidence based practice is required for doctors to cope with EBM, but growing enforcement of EBM "standards" might be dumbing down our doctors.
While there are good reasons for using dbRpCTs as a higher grade of evidence for clinical efficacy of treatments, this is not applicable to non treatment studies, such as investigatory ones. You also need to understand why cbRpCTs are necessary. dbRpCTs are double blinded randomized placebo controlled trials. Each part of that reduces risk of particular bias. However there are many biases still left. Cookie cutter approaches to EBM, such as used by the team assembling the review of the P2P blatantly ignore other biases.
They ignore that there is risk of allegiance bias. This is closely tied to a bias in publication reviews if only a small number of reviewers, with high allegiance, are doing the reviewing.
They ignore that there is risk of bias from failure to double blind. The fact that psychopsychiatric interventions may be hard or impossible to double blind does not matter.
They ignore that there is risk of bias from failure to use a proper placebo response. Again, psychopsychiatric interventions cannot be placebo controlled. They can however control against a no interventions group. PACE needed an additional control arm.
They ignore that there is risk of methodological bias.
They ignore that there is risk of bias in subjective data, especially for outcomes. PACE gave people many months of psychotherapy then asked them how they feel about what was done.
NO psychopsychiatric study is of the highest grade of evidence. ZERO. Its a big fail, which the cookie cutter approach cannot cope with.
With such a cookie cutter approach contrary evidence can be dismissed as "lower grade" evidence.
Lets look at another issue. Biomedical research on this disease is in its infancy. Funding levels are so low that research on ME and CFS get about the lowest level of funding per patient of any common chronic disease. Few researchers are doing the research, and very few institutions back their researchers properly.
This means the entire field of research is very new and underdeveloped. Cookie cutter EBM approaches, on a tight budget and to a deadline, cannot deal with this.
Quite aside from biases from economic imperatives or broad pressures from BPS ideology, there is a big issue with Zombie Science here. That is, the deck is stacked by priority funding going to favoured areas, that research being of lower quality but sails right through because of entrenched bias. I am of course considering the PACE trial as an example. When large numbers of RCTs, and most notably not dbRpCTs, are in the mix, and ineptly given a high standard of evidence, other things can pale in comparison. Yet such studies do not look at each of these in great detail. For example, the P2P review gave PACE some praise, but this study is of such low quality, with so many demonstrable flaws, that I think all the papers should be retracted.
With some rethinking, rewriting, and after some feedback, I might blog this post.