Thanks for the study. I agree on all points. This is the challenge with sociological research: it is unethical to conduct controlled studies. We will never have controlled IQ research. The study suggests we continue to perform better quality primary research, and I fully agree. Until then, as per the data in the study, the correlative evidence remains compelling. At least as far as sociological research goes.
I tend to think this research is more compelling and useful at the macro level. We should bear in mind that the correlative coefficient between IQ and income is only between 0.2 and 0.4. There are many other factors which also impact outcomes.
That is, surprisingly, incorrect. A meta-analysis by Strenze (2007) showed that the predictive power of IQ is slightly stronger than that of parental socio-economic status (SES) (Table 1). Specifically, IQ measured before age 19 outdoes parental SES in predicting future educational attainment, occupational status, and income after age 29 (see “best studies” on Table 1). In other words, if you want to predict an adolescent’s success in adulthood along a given metric of success (e.g., income, educational attainment, or occupational status), it is more useful to know that adolescent’s IQ than to know the success of their parents along that same metric. In the conclusion of the analysis, Strenze (page 416) argues that this would be unexpected if the predictive power of IQ could be attributed primarily to its association with parental SES:
The meta-analysis does find that parental SES also correlates significantly with the future outcomes of the child. However, because youth IQ and parental SES are correlated, it is possible that some unspecified portion of the predictive power of youth IQ is due to its correlation with parental SES (or vice-versa). To get a more precise estimate of the effects of youth IQ (independent of parental SES), we need to estimate the predictive power of IQ after controlling for parental SES.
Success is undoubtedly multi-factorial. Who you know is important. So is parental educational achievement, access to nutritional food, an absence of violence in the home, IQ, etc.