And they're a segment of the population. To study the result of a population receiving a BI, there's plenty of data.
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.
You can't of course study the impact on the economy, but you can surely understand how people change with the UBI.