The book Altered Traits goes over a lot of the scientific results, I think it's two chapters of the book that cover this stuff. One of the studies they cover studied people who had never meditated, people with 10,000 hours and people with about 36,000 hours of meditation if I recall correctly. This last group is the one that exhibited altered traits, and it's not easy to find people with this many hours of practice, hence why they reuse the participants. All other participants exhibited some of the altered traits but only during intense meditation periods, the master meditators exhibited them all the time.
The results from the book are/study are hard to interpret, something about sustaining gamma waves for long periods of time and having younger brains in those that practiced meditation a lot. They also recovered from pain faster, and wouldn't develop anxieties about it.
Since these subjects are very interesting, it makes sense to study them again with different techniques or reproducing previous results.
> it's not easy to find people with this many hours of practice, hence why they reuse the participants [...]. Since these subjects are very interesting, it makes sense to study them again with different techniques or reproducing previous results.
That's fine as far as it goes. It helps us confirm that a phenomenon can actually occur and perhaps tells us something about its general shape. But when studying a population of known outliers, it's not credible to assume how the results will or won't apply to a broader population. This isn't an abstract epistemological concern; scientific journals are absolutely packed with exciting preliminary findings that vanished into insignificance when somebody did a larger or more rigorous study (but nevertheless might be cherry-picked for a pop-science/self-help book based on the "revolutionary" findings).
The results from the book are/study are hard to interpret, something about sustaining gamma waves for long periods of time and having younger brains in those that practiced meditation a lot. They also recovered from pain faster, and wouldn't develop anxieties about it.
Since these subjects are very interesting, it makes sense to study them again with different techniques or reproducing previous results.