Sure, 'smarter' was a poor choice of words, but the point is I suspect there may be a correlation between general cognitive performance and job attainment.
EDIT: I guess the trick might be to not use a survey, but to give the participants all the same project to work on (very expensive), then adjust the results based on their previous performance. I think an ideal group for this would be students because they're all already working on the same projects. Tell one (random) group that they can have some money if they promise to work on their class project for no more than one hour a day. Could this work?