What's the evidence that results of such study could be generalized to the entire population? I mean, yeah, 2000 people seem like a big group, but one might hav

What's the evidence that results of such study could be generalized to the entire population? I mean, yeah, 2000 people seem like a big group, but one might have different ideas about what to do with free money if the society around stays exactly the same vs when everybody else is also entitled to UBI. When I'm unemployed and look around and see all my friends work I might feel quite ashamed of myself and willing to change, but if all of them "retire" at 30 instead this might not be exactly the case.