Interesting....Although some of the things mentioned above are plausible, I think a bigger reason could be that depression is identified in white collar workers more. For instance, to afford psychiatric care 1) you would need to have enough insurance and/or $$ 2) you need to have enough exposure to discussions about depression so that you would wonder if you have depression yourself. For instance if all your friends see a shrink, you would be more likely to see one too. 3) you also need to be educated enough to understand that if there is something wrong, you need to get help. So I think, it's rich and well educated people who tend to be DIAGNOSED more. In other words, the blue collar workers may still be depressed, the only difference being that they do not know how important it is to get help or that they do not have the resources. If this was published in a major medical journal, it should have talked about the things I just mentioned. If it did not, it was probably published in a crappy journal, and I would take the findings with a grain of salt. Btw, can you provide the reference? I am not a medical guy, but this is interesting.