Thanks, good comments. I very much agree with the first point. It is very important to pay attention to connotations. I'll put some serious thought into what terms to use if I get around actually doing this.

I agree with the second point too. It's not that far-fetched regarding many questions. For instance, it seems to me that people who are right-wing and left-wing, respectively, when they are young, tend to choose careers on different bases. Right-wing people tend to want to earn more money than left-wing people. Thus to some extent they earn a lot of money because they are right-wing, rather than are right-wing because they earn a lot of money.

You could give various further questions intended to distinguish "selfishness" from other explanations of the correlation; for instance, questions regarding your views have changed as a result of changes in interest. In practice, this might be hard to do efficiently, though.

I guess, though, that if you have a sufficient number of questions, and your political views consistently correlate with your interests, then it'd be hard to explain this with anything but "selfishness".

I agree with the last point, also, that the score would need to be accompanied with a thorough discussion of how to interpret it. For instance, a left-wing feminist member of NAACP who is also a working class African-American female might be given the same selfishness score, on this test, as a low-tax anti-feminist racist who is also rich, white and male, but most people would find the former pattern of preferences less objectionable than the latter.