Why would people expect 100% participation in the extension trial
I mean seriously people, 100% participation is unrealistic for many reasons. But the most important reason is they answered the question "what's in it for me?" with the response "not enough." Now why would 1/3 of the participants that had a break from the trial determine there was "not enough" to continue? Why would 1/3 of a population not continue when 1/3 of the population was getting a placebo?
Now a better question is why would 100% of the recently completed protocols continue? Strong encouragement from the physicians conducting the trial would help convince people on placebo that maybe they want to give up another year of their life trying something (as yet) unproven that they've seen no benefit from as yet..
A sizeable part (50% ?) of the patients is on placebo. It would be strange if they would all participate in the extension trial. AFAIK it is not an open label extension, so more than 50% participation is good for safety, but maybe also a hint of a placebo effect.
Wouldn't the 'decision makers' of these trial participants be the caretakers and not the enrolled patients themselves? If so, the caretakers would be the ones seeing benefits and determining the value of continuing. If the decision to continue in the trial is determined by the patients themselves, at the early stages of AD, I would question the value of trying to impute any logical rationale for the retention percentages. I am curious who is making this determination...enrolled AD patient, or someone on their behalf.
100% because most of us believe the PBt2 drug is that good and so we pass that belief onto future trial participants. I believe that there were no late stage AD patients. I believe in future, any extended trial should be unblinded so that all participants will know they are getting the real deal on the extension after having given up a years worth of their time on the original study. That information about decision making may very well be in the results information. good question!