June 27, 2007

Brothers and IQ, again

Something that's important to keep in mind in all the hoopla over the Norwegian study of conscripts showing a few point higher IQs for oldest brothers, with the New York Times running three articles on the subject over the last week, is that small differences in IQ scores like this can be influenced by methodological issues of specific tests.

Now, big differences in average IQ, such as 15 points (one standard deviation), are test-independent. For decades, the Holy Grail of cognitive test designers has been to invent a test on which blacks and whites would average the same, without losing most real world predictive power. The first psychometrician to accomplish this would be rich and celebrated. Unfortunately, it has turned out to be the equivalent of the perpetual motion machine for engineers and cold fusion for physicists.

But small differences are sensitive to test design trade-offs. For example, the U.S. military's 1979 version of its very heavily g-loaded entrance exam for enlistment applicants, the Armed Forces Qualifying Test, found an anomalously large 18.6 point gap between whites and blacks when it was standardized on the National Longitudinal Study of Youth in 1980 (this is the study that provides much of the new data in The Bell Curve). The average study has found a 16.5 point difference, so this 18.6 point gap was strange because the AFQT is a test the military has spent a fortune developing, and the NLSY sample, with about 13,000 participants including an oversampling of minorities, was the gold standard for a nationally representative data set..

The 1979 AFQT was designed to be highly accurate around IQs of 100. For instance, from 1992-2004, the military took very few applicants with IQs of 90, but would take quite a few 95s.

So, the 1979 AFQT was designed to be extremely thorough for the average person: it was 105 pages long! As Charles Murray pointed out recently, in the 1990s it was finally realized by studying results on a question-by-question basis that the length of the test had a downside that explained the unusually large 18.6 point white-black gap. Low IQ applicants, especially black males, often got discouraged by all the questions they couldn't answer and would give up, either not filling in the rest or bubbling in the rest of the way.

In 1997, the 105 page paper and pencil AFQT was replaced with a computerized test that dynamically changed the test to reflect performance so far. For instance, if you missed a lot of early questions, the computer would serve up easier questions. The white-black gap turned out to be 14.7 points on the 1997 normalization of the computerized AFQT.

Unfortunately, we don't know enough to be able to divvy up this 3.9 point narrowing of the white-black gap from one version of the AFQT to the next between the test methodology change and actual change in the size of the gap.

Somewhat similarly, Half Sigma hypothesizes that the brother result on the Norwegian equivalent of the AFQT is caused by older brothers being more conscientious. Perhaps they study harder in school and thus do better on the parts of the test that are less g-weighted. Or perhaps they just don't give up as easily.

Or this could be a real result.

The point is, however, that it's exactly backward for the media to get all worked up over one study reporting a 3 point difference between demographic groups (older and younger siblings) while ignoring the dozens of studies reporting much larger differences between demographic groups, such as between whites and Hispanics -- especially because the Senate is voting on an immigration bill right now!

The best estimate I've yet seen of Hispanic-American IQs is the 2001 meta-analysis by Roth of 39 studies covering a total 5,696,519 individuals in America (aged 14 and above). It came up with an overall difference of 0.72 standard deviations in g (the "general factor" in cognitive ability) between "Anglo" whites and Hispanics. The 95% confidence range of the studies ran from .60 to .88 standard deviations, so there's not a huge amount of disagreement among the studies.

One standard deviation equals 15 IQ points, so that's a gap of 10.8 IQ points, or an IQ of 89 on the Lynn-Vanhanen scale where white Americans equal 100. That would imply the average Hispanic would fall at the 24th percentile of the white IQ distribution. This inequality gets worse at higher IQs Assuming a normal distribution, 4.8% of whites would fall above 125 IQ versus only 0.9% of Hispanics, which explains why Hispanics are given ethnic preferences in prestige college admissions.

In contrast, 105 studies of 6,246,729 individuals found an overall average white-black gap of 1.10 standard deviations, or 16.5 points. (I typically round this down to 1.0 standard deviation and 15 points). So, the white-Hispanic gap appears to be about 65% as large as the notoriously depressing white-black gap.

So, the white-Hispanic IQ gap is about what you'd guess from observing life around you with your lying eyes: not as big and deleterious as the white-black gap, but not trivial either.

If a 3 point IQ difference between brothers is worth three articles in the New York Times, you might think that an eleven point gap between whites and Hispanics would be worth, oh, say, eleven articles, especially when the immigration bill is up for debate in the Senate. But almost nobody has ever mentioned Roth's finding in the press.


Anonymous said...

you're in extremely dangerous territory talking about "hispanic IQ". unless you're talking about the mean IQ of spain, you're not talking about anything real.

talking about "latino intelligence" in reference to anything other than europeans is absolutely meaningless, and the data should be thrown away or ignored.

Svigor said...

For decades, the Holy Grail of cognitive test designers has been to invent a test on which blacks and whites would average the same, without losing most real world predictive power.

I wish they'd go ahead and blatantly tailor the "cultural" aspects of IQ tests, SATs, etc., to blacks. After a quick correction non-blacks would bounce back, and liberals would lose their argument about cultural bias (not that they have much of an argument, of course).

Steve Sailer said...

Jody, everybody today uses self-identification. If an individual checks off the Hispanic/Latino box, they are Hispanic/Latino. Self-identification is the most politically relevant way to group people.

Luke Lea said...

Now that the facts are in, more or less, it's time to start trying to figure out what kind of society can provide productive and satisfying lives for all these different kinds of people. Personally, I don't want a world with a lot of servants in it (or, to paraphrase Lincoln, as I would not be a servant, so I would not have a servant.)

I suggest the answer is a much shorter work week in the manufacturing sector, using more labor-intensive and less robotisized work processes that are still within just about everybody's purview to do, with the rest of the time spent being one's own servant (ie, doing one's own cooking, child-raising, cleaning, home maintenance, etc., with lots of sports and local politics for entertainment) and allowing the cognitive elites to handle the more demanding managerial tasks of keeping the whole shebang on the road.

In other words, factories in the countryside run on part-time jobs. In other words, happiness is a part-time job in the country. for more see here: http://luke.lea.googlepages.com/home

sorry, steve, I just had to put that in. Charles Murray, are you paying attention?

Anonymous said...

talking about "latino intelligence" in reference to anything other than europeans is absolutely meaningless, and the data should be thrown away or ignored.

Why would it be relevant in talking about European intelligence yet not relevant in talking about the intelligence of anyone else? Do you think 1 + 1 = 3 in "Latino math?" Have you ever seen the sort of questions on an IQ test?

Unknown said...

I see your point, Jody. Who are the Hispanics? I presume these IQ tests are done on the population of South Americans who have migrated to the US - a different racial mix than in Spain.

Hispanic is ethnicity without much reference to race though you can identify subgroups of Hispanics who belong to different identifiable races or at least racial mixes.

Marie Everington said...

'Culture' is a term of uncommon slipperiness. It tends to be highly subjective in both definition and application (as in intelligence testing).

If black people think in a different way, or valued different uses of one's brain, as examples, this is not something that would be reflected in current tests used as intelligence-measuring proxies.

I don't really mean the 'multiple intelligences' stuff that is mostly feel-goodism-- I mean that testing metrics as devised often tend to reflect unconscious biases in the thinking of the test designers. Such as divergent ideas on what behaviors and actions constitute reflections of 'culture' or 'intelligence'.

If my culture rewards problem-solving methodology A and the IQ tests refer exclusively to problem-solving methodology B, then I might well look like I am not as 'intelligent'.

I think you understate the level of myopia and fearmongering surrounding intelligence testing. Nobody genuinely wants to deviate from current established metrics, whether they accurately reflect cognitive ability or merely a particularised subset of cognitive ability.

Anonymous said...

Based only on personal experience, I have no problem with the findings of the Norwegian study. Having known lots of large Mormon families, I have seen firsthand the effects of birth order on such families. In my experience earlier born children tend to be more responsible, more conservative, more likely to graduate from college, and more likely to stick with their religious upbringing.

Partly I suspect this is because older children are given more responsibility froma young age, partly it's due to older children having recieved more attention when they were young, and partly I suspect it's due to parents just getting tired of being parents. My parents were very strict with my oldest siblings. By the time they got to me they (pretty much) just said "Do whatever."

I think a Norwegian type study on larger families (5+ kids), might throw more light on whole the subject.

Anonymous said...

The term "Hispanic" pertains to people or things from, or pertinent to, Spain.

"Latino" is a little vaguer but as I would see it it could be applied to Italians, French, Spanish, Portuguese, or anyone else from a part of Europe originating in a region where Latin was the lingua franca, so to speak.

Mexicans and other Central Americans are mestizos, unless they are pure Indios, and we see more and more of those here these days.

Puerto Ricans are mulattoes.

Anonymous said...

I used to believe this nonsense before I went to a gym and met many blacks, or met many artistic, creatve Hispanics. We are just different in our own ways, not less or more inteligent than one another.