Trial Report Videoconference-delivered group cognitive behavioral stress management for ME/CFS patients who present with severe PEM: a RCT, 2023, May

Was able to read the paper today (it is now open-access) and it seems that Sid suspicion was right: this is a post-hoc subgroup analysis because the original analysis found no effect. The authors write:

 

Post-hoc = deciding to run different analyses than what you said you would do, after you’ve got the data from the trial

Subgroup = dividing the participants into new types of groups, sometimes quite randomly

Both are potent sources of bias.

 

Open access here: https://pmc.ncbi.nlm.nih.gov/articles/PMC11086677/

 

To align with a clinically useful perspective of PEM status (i.e., presence vs. absence of the symptom, as in case definitions) we dichotomized the PEM intensity variable into highPEM (Severe, Very severe) and lowPEM (Very mild, Mild,Moderate, not endorsed) categories [see 20 for additional rationale for this classification].​

20 is this:
https://www.s4me.info/threads/pem-i...ith-cfs-2019-may-fletcher-klimas-et-al.12900/

By PEM, they mean this (based on Fukuda):

The item regarding “unusual fatigue following exertion that lasts for at least 24 hours” served as an index of PEM status and was removed from symptom frequency and intensity score calculations.​

 

For reference, I believe the CDC CFS Symptom Inventory is worded something like this:

During the past month, how bad was your fatigue after exertion?

• N/A
• Very mild
• Mild
• Moderate
• Severe
• Very severe

​

It seems to me like it isn’t really appropriate for dividing people into groups of severity..