The typical null hypothesis at the outset of the experiment is that no difference exists between the control group and experimental group (for the variable being compared).So on that basis, I would formulate the following null hypothesis for ME/CFS:
There exists no relevant difference between patients with ME/CFS and a healthy control group.I'll just point to the work of Kathleen and Alan Light showed repeatedly that we can reject this null hypothesis. There exists a relevant difference between patients and a healthy control group – CFS patients are not healthy.
So we need a new null hypothesis:
There exists no relevant difference between patients with ME/CFS and patients with similar medical conditions.So the first two medical problems that came to mind for Kathleen and Alan Light were deconditioning and multiple sclerosis. Again, they rejected this new null hypothesis – CFS patients are distinguishable from deconditioned persons and they can be distinguished from multiple sclerosis patients.
Another condition that is similar is Fibromyalgia. Now, it got interesting. With their biomarker, they found a significant overlapp between ME/CFS and Fibromyalgia. Many (but not all) patients with CFS have Fibromyalgia as well. Many (but not all) patients with Fibromyalgia have CFS as well.
It comes down to that "The Lights" say that they have a biomarker, that they can distinguish CFS patients both from healthy controls, and from some similar medical conditions, but barely from Fibromyalgia patients. (It is not a perfect biomarker, but it looks promising)
So we can not fully reject the last null hypothesis. What would a new null hypothesis on this basis look like?
ME/CFS and Fibromyalgia are overlapping illnesses from the same spectrum, but distinct from other illnesses.I guess we need more research.