just looking for a rough sketch
Well, you can probably go about it in the following way. IQ is and was a controversial concept. One of the lines of attack against it was that it is meaningless, that the number coming out of the IQ test does not correspond to anything in real life. This is often expressed as "IQ measures the skill of taking IQ tests".
To deal with this objection people ran a number of studies. Typically you take a set of young people and either give them a proper IQ test or rely on another test which is a decent IQ proxy -- usually the SAT in the US or one of the tests that the military gives to all its drafted or enlisted men. After that you follow that set of people and collect their life outcomes, from income to criminal records. Once you've done that you can see whether the measured IQ actually correlates to life outcomes. And yes, it does.
I don't have links to actual studies handy, but you can easily google them up, and you can take a look at a not-fully-rigorous description of the various tiers of IQ and what do they mean in real-life terms.
Basically what these studies give you is the cost of an IQ point, cost in terms of a lot of things -- income, chance to end up in prison, longevity (high-IQ people are noticeably healthier), etc.
Given this, you can calculate the expected outcomes for the US black population. If their average IQ is 10-15 points lower, you can translate this into expected income (lower than the US mean), expected chance of a criminal conviction (higher than the US mean) and other things you're interested in. Once you've done that, you can compare your expected values with ones empirically observed. Any remaining gap will be due to something other than the IQ differential.
informs your politics
On a macro level it does not. There are smart people, there are stupid people, and the correlation to some outwardly visible feature like the colour of the skin doesn't matter much. I am not a white nationalist, I do not think the Europeans should re-colonise Africa for the natives' own good, etc.
On a micro level it does. For example, I find affirmative action counter-productive. For another example, I don't believe the claims that inner-city schools (read: black) lag behind suburban schools (read: not black) because of lack of funding or because of surrounding poverty. Throwing money at the problem will achieve nothing.
There are smart people, there are stupid people, and the correlation to some outwardly visible feature like the colour of the skin doesn't matter much.
How do you mean? You're saying you believe it to be true that, generally, people with black skin color are more likely to have a significantly lower IQ than people with white skin color... And you believe that IQ is correlated with life outcomes. How can this not matter much?
I find affirmative action counter-productive.
I also have the sense this may be true in many instances. The theory seems solid, ...
If it's worth saying, but not worth its own post, then it goes here.
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