Via Steve Sailer, I read Half Sigma's theory about how your career success depends on your parent's socioeconomic status the most when you have an above average intelligence:
IQ is more highly correlated with life outcomes for people with below average to average IQs. Most career tracks have an IQ floor, and if your IQ isn't high enough to meet the floor level, you can't perform that job adequately. Few career tracks have IQ floors much higher than 115, so if your IQ is higher than that, your parental wealth and connections become very important.
Thus, the higher your IQ, the more important the wealth of your parents becomes (the very opposite of what most people think). People with exceptionally high IQs but inadequate parents often have poor life outcomes because of the mismatch.
I'll use the General Social Survey ten question IQ test as well as its father's socioeconomic status index (PASEI) and the respondent's income to assess the hypothesis. The 100-115 range seems to be a grey area, so I'll compare the group below that with the group above. To be precise, the two cutoffs I'll go with are 98 and 112.
My reasons for this are two-fold: 1) there are only 11 possible scores on the IQ test (0-10 out of 10 correct) so there are only 11 scores to choose from as cutoffs--98 and 112 are two of those possibilities; and 2) the highest score is only 125--the next lower score is 118, then 112, but I don't want the cutoff to be 118 since that gives very little variation within the high-IQ group.
OLS regression coefficients are shown above (N =1,335). First, the effects are surprisingly weak. I suspect that this is due in part to the truncated IQ measure--the high-end variation is all squeezed together--and the truncated measure of income (the GSS focuses on low income folks, and lumps all those making $110k or more together).
The Betas indicate which indepedent variable has the greater influence, IQ or father's SES. For the low-IQ group, IQ is close to being as strong as social class, and both effects are statistically significant. In the smarter group, IQ drops to non-significance. The effect of social class is weak, but it manages to teeter on statistical signficance at the .05 level.
So, Half Sigma's idea is supported here, but I wouldn't be surprised if the results were stronger if we used occupational prestige instead of income since it is more normally distributed. Maybe I'll look at it later if I find time.