The key is to shroud the treatment among others that are low-risk with clear short-term benefits and thus make it impossible to attribute specific improvements to specific treatments. For example, end a treatment session with a massage and ask for treatment feedback either during or immediately after the massage.
Two more examples follow. The first leans towards the unscrupulous; the second is more innocent and accidental, and it shows the challenges of trying to subtract out this influence.
Stem cell therapy for SCA
There are in-patient clinics that will take (e.g.) ataxians for (e.g.) 25 days and give them the best, modern physical therapy imaginable (including changing their diet) by smiling and friendly therapists. Nearly every moment of those 25 days will revolve around physical therapy. They charge USD 50,000 to 200,000 for the experience. Why so expensive? Because they include stem cell injections. Here’s a recent story:
The physical therapy alone would undoubtedly have noticeable benefits. There’s no question: something will have improved after 25 days. The unknowns are how long the improvements will last and to what to attribute the improvements.
SCA drug trials
Even if participants are not encouraged to get more physical therapy during a drug trial, some will do it—maybe even try to get their lives in better order and do some things they’ve been putting off for weeks, months, or years. Surely, SCA drug trials can’t require that participants attempt no other improvements to their lives, especially when they could be on a placebo for a long duration.
Pushing yourself harder when trying something new is natural. For example, if you walk four laps before trying something new and five laps after, it’s tempting to attribute the new thing to being able to walk more. But for such slim gains in the context of an overall downward SCA spiral, it could be that trying something new has only inspired you to do a little more than usual.
It doesn’t surprise me at all if a placebo tests better than an SCA drug in the short term, especially if the best case for the drug is to show modest and temporary gains in some people. Assuming the drug is not detrimental to anyone, it just means that of the various things in their lives that they’re working on improving, something is showing short-term payoffs.