good question.
the carrier population had a high incidence of an SAE called vasogenic edema, after which doses are held, and they possibly thought this interfered with ability to detect difference. same size was also reasonably small.
i don't have a good answer. that's why i think the odds of success are pretty low in this population in mild to moderate AD. However, I do think if they treated carriers earlier in the disease, say prodromal or MCI, bapineuzumab would have a good chance of working.