A tale of a convenience sample with inconvenient serious limitations.
The study has too small a sample to warrant a manuscript submitted to a peer-reviewed journal. If you keep looking at it, its problems get compounded.
I recommend downloading this open access article and following me as I explained its flaws.
What, too small a sample? With 2147 patients, the study is probably the largest ever of mortality among patients with chronic fatigue syndrome. But the adequacy of sample size is determined not by the total number of participants, but the number having particular events, in this case, the relatively rare events of mortality and suicide. In the seven-year follow-up, there were 17 instances of all-cause mortality, 11 among women and six among men. There were five suicides, three among women and two among men.