And in particular, if they know they cannot count on the basic income indefinitely? Studies on this in the past have hit that exact problem.

I think if a basic income is eventually introduced nationally it will be the result of a hard-fought political battle with many proponents and detractors, and there are plenty of cases of laws like that being reversed within a few years.

I don't know this would be too unrealistic for the study.

Studies typically have a set duration. If you offer people a basic income for the duration of the study, they'll need to plan differently than if they have some reasonable chance of having a basic income indefinitely.

This is certainly true. However, for many cases there may be little difference. A year or two of basic income is sufficient to start a business, learn skills to enable a career switch (exceptions, of course), care for a newborn, deal with short-term illnesses, etc.

That's always a hard thing to tease out of psychological studies. The tests have to be very clever to do so, and they'd have to be wide ranging. Essentially, yes, but it'll cost a lot of money.