Dr. J, a good friend with expertise in psychometrics commented on the Richwine thread. In broad strokes this was my impression, but she's got a lot more detail:
"A few points here (a little late, and also WRT your prior post on this issue):I reiterate my advice to economists: by all means throw anything even resembling an intelligence test on the right hand side of the equation if you've got it. It's important heterogeneity worth controlling for. But then you're probably best served ignoring and leaving the interpretation to others because it's questionable whether we really have the chops to talk about it.
If IQ is highly determined by genetics (I defer to the geneticists on this): I believe current research shows it's about 50% genetics, 50% environment (most of the latter being non-normative social experience, that is, not the parents)
IQ is messy, messy, messy. It is a pain to operationalize. Many times, IQ is defined as "general intelligence" -- but what is intelligence? Well, whatever intelligence tests measure.
Other hitches: IQ tests were primarily, if not entirely, developed in the Western world, America in particular. How can we -- unless we are narcissistic ego centrists -- assume that what our society considers is intelligence could really generalize across cultures? And indeed, cross-cultural research pretty routinely reveals that different cultures prioritize different aspects of the human experience; many cultures have words for concepts that are not prominent/discussed in American society. So we might expect cross-cultural differences in scores on IQ tests; that doesn't mean necessarily that people differ on "intelligence", broadly construed. That just means it's ridiculous to expect measurement invariance of a western concept across all cultures.
And also, often, IQ tests are standardized around 100. Constantly standardizing test scores makes it a little difficult to look at changes over time.
Finally, we know that tests -- especially IQ tests -- test both "intelligence", but, to a large extent, also the ability to take tests. This is why, even within the US, we have sub-group differences in IQ. Because different groups have different access to the experiences necessary to develop testing competence. Now, we are working to develop culturally-ungrounded IQ tests (such as the Hannon-Daneman test or the Siena reasoning test), and these tests do help mitigate/decrease sub-group differences in American samples. But, you can see . . . this is a hot mess.
I think IQ is one of the most tricky areas of inquiry in psychology, actually, because in normal everyday conversation we all think we have a sense of what it means, but psychometrically it's fairly problematic. Which does not mean we can ignore it -- it's a great concept and a lot of great work has been done on it! -- but it does mean we have to discuss it in as many forums as possible!"