Having lived in Marin County for the last 7 years, I can tell you that a less heterogenious mix of people will be difficult to find. This is one of the most elite, wealthy, insular groups of individuals gathered in one geographic area. As an example of just how insular this area is, The Marin Independent Journal put a story on the front page a few years ago about an individual that had dared to put up a billboard which is against a county ordinance. If this type of news can make it to the front page, what can I tell you? To take only 60 from this rarefied group and extrapolate the findings to apply to the rest of the population... is disturbing. This just shows that Wallerstein hasn't made it out of Marin County (having been educated at UC Berkeley) and doesn't have the perspective to speak to how the US population as a whole might be affected.
It's about time we see a study based on a much broader and more representative base than Wallerstein's.