[notsureifwant]

My personal interpretation is that a lot of this effect is driven by the fact that income (which I think we tend to think about as a proxy for standard of living, including quality of school system and safety of neighborhood, and not just what their family can buy) is often difficult to measure, and parental education might actually offer a much better measure of "standard of living" children experience (which is why it may show up as significant, while income may not, in those analyses).

[joshvm]

Wealth is a poor indicator of education. Usually the questions will be how much do the parents earn, rather than where they live or their standard of living. My Dad has a doctorate in physics from a top university, yet he's pretty much given up normal employment and lives a happy sustainable life. Measured by annual income alone, he's probably below the poverty line.

[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.