[qq66]

On an individual scale, wealth is a poor indicator of education, but in the aggregate the correlation is very strong: http://www.bls.gov/emp/ep_chart_001.htm

Doctoral degree-holders are unique in that they're the only group that earns less than a lesser-educated group (professional degrees).

[cperciva]

A professional degree isn't exactly "less" than a doctorate, though. Traditionally speaking, Medicine and Law are doctorates... and they both rank ahead of the Doctor of Philosophy (but behind a Doctor of Divinity, which is the highest doctorate).

[dragonwriter]

> Traditionally speaking, Medicine and Law are doctorates... and they both rank ahead of the Doctor of Philosophy

No, while medical doctors and lawyers (civil doctors), were recognized uses of the term "doctor" for quite some time, traditionally the professional degrees in both fields have been baccalaureate degrees (the MBBS in medicine/surgery and the LL.B. in law), outside of certain Scottish universities, and the change to make the degrees generally doctorates were fairly recent (19th Century) US innovations.