My concern is that they are going to struggle to get 20,000 people given the limitations in criteria. The two headline numbers I know of in regards to ME/CFS prevalence are that about 0.2% have ME/CFS, about half of which meet the Candian Criteria and that 90% of patients are undiagnosed. When you further filter that cohort with comorbidities you potentially don't have a very large group especially since initially you are recruiting in the UK. 65,000,000 people, 0.2% of which have ME/CFS leaves 130,000. With only 10% being officially diagnosed by their doctors you only have a maximum study based on doctor diagnosed of 13,000. Then you filter off common comorbid conditions like hypothyroidism and such and well its going to be a struggle to get to 20,000.
There are a lot more Long haulers with ME/CFS but there are only maybe 30,000 with a diagnosis and its for Long Covid not for ME/CFS, so they don't meet the criteria either. I hope DecodeME has a lot better information about the real diagnosed prevalence of the condition and that in practice they have more than enough candidates. From the historically published papers its a problem or the situation has some how changed dramatically in the last year despite most people reporting the guidance hasn't changed much. I think its a bit of an ask to expect 150-200% of the available patients to participate, it necessitates going off to Europe to find participants, which will themselves be diagnosed under a different criteria to those in the UK. I also think the comorbidity filtering likely drops the vast majority of severe ME patients as well. Are the mild patients the best ones for this data? I am not sure that is a good idea.
I have issues with how the participants are being selected, if we lived in a reasonable world then it would be a less flawed criteria but I live in the one where this gross widepsread systemic prejudice as the research data shows.