It's not just a tiny group. It's the most influential group of 9 people at the very top of an egalitarian system of law. Do they represent all of us? No, not perfectly. They should represent the best of us.

One reason that this study exists is that it's a deliberative body with excellent records. It would be great if longitudinal studies of huge populations existed, but that would require ridiculously expensive (and highly invasive) data acquisition.