Which of them completely displaces means-tested welfare to provide the support floor for all who are in the eligible population. Social Security doesn't. Pensions don't. Being idly rich might, I suppose, in that that is just “living of capital” but ignoring all the people who don't have a lot to live on.

> And they're a segment of the population. To study the result of a population receiving a BI, there's plenty of data.

Not relevant to UBI there isn't. Some segment of the population receiving income varying a Ross indiciduals based on their past work and investments isn't even loosely similar to the whole population of a community receiving equal unconditional UBI, and there is little reason to expect the former to provide much insight on the latter.