My vague hunch would be that identical twins reared apart tend to often both be raised about the 25th percentile of income. Say, identical twins are orphaned because the parents are killed in a car wreck or the parents both become drug addicts or whatever. So the extended family, maybe both sets of in-laws, gets together and says, "OK, I know this will be a major sacrifice, but we've got to dig deep and figure out who can afford to raise the two kids."
But nobody has the money to take both, so one couple takes one twin and another couple takes the other.
So, there don't seem to be too many Prince and Pauper-style examples of identical twins being raised apart at different ends of the social scale, because if one relative is really rich, she'd probably take both twins.
Sorry if dumb question but, would the same person/same genetic theoretical individual, one raised poor and one raised wealthy, score identically on IQ tests?
It’s a controversial topic, but I support the view that malnutrition does lead to lower IQ as an adult, though empirical tests of the hypothesis have been disappointing.
Illiteracy is probably a big one, too. The harder it is for one to read, the harder it is to maintain a large vocabulary, or review information. The smaller the vocabulary, the harder it is to sharpen one's thinking, understand abstract concepts, communicate ideas, or solve problems.
But I don't see further educational literacy efforts making much difference. There's still only so much you can do when someone's in the 80s and below, so I really do think gene therapy will be the only truly effective means to solve the Third World's low-average-I.Q. problem.
The only problem with this looking at identical twins reared apart is there is still a womb effect. How much of our intelligence is actually shaped by the conditions of the mother's womb having an effect on the brain?
Embryo splitting is done regularly in cows and creates identical twins. In theory one could split a human embryo, implant the resulting identical twin embryo in different moms and compare.
A lot of effort for a study unlike to pass the IRB and given the results above I doubt the womb effect is a big thing unless moms smoke crack.
Do we know to what extent the heritability varies? Is it additive? For example, if the dad is high IQ and the mom is low IQ, are their offspring likely to average out in the middle or inherit either high or low IQ? If both parents are high IQ, do their kids have an increased chance of having an even higher IQ than either parent?
"If both parents are high IQ, do their kids have an increased chance of having an even higher IQ than either parent?"
No. On the contrary the kids are more likely to regress closer to the mean of their ethnic group. But with luck or enough kids it is likely that some will be higher IQ than their parents.
For the less knowledgeable among your readers: I suppose that test reliability is estimated b the correlation when you test the same person twice. Correct?
I found some more context on Wikipedia, because this also interested me, being a psychometrics-outsider, as it were. I believe the idea that Hyperdupont refers to would be like using "parallel tests" to estimate reliability ("parallel" because you wouldn't actually want to give the same person the *exact same* test twice with the same questions on it, because they'll remember them; it would have to be a "parallel test" with different questions but the same score expectation and variance).
The Wikipedia article on Classical Test Theory elaborates:
> Using parallel tests to estimate reliability is cumbersome because parallel tests are very hard to come by. In practice the method is rarely used. Instead, researchers use a measure of internal consistency known as Cronbach's α.
> Cronbach's α can be shown to provide a lower bound for reliability under rather mild assumptions. [...] Thus, this method is empirically feasible and, as a result, it is very popular among researchers.
And when you refer to reliability-adjusted correlation, is that like an errors-in-variables adjustment where you use the reliabilities to estimate the measurement error in the predictors?
It’s a little unsatisfying to just assume the .91 reliabilities for so many of the tests, but at least a decent chunk of your N has empirical reliability estimates.
>And when you refer to reliability-adjusted correlation, is that like an errors-in-variables adjustment where you use the reliabilities to estimate the measurement error in the predictors?
My apologies if I've provoked your curtness somehow :(
I was just asking if this:
> The mean correlation is 0.7, mean reliability-adjusted correlation is 0.77...
... referred to disattenuation, i.e., correcting for the dilution that results from considering the individual-level IQ measurements to be noisy variables themselves, enabled by the reliability estimates, which tell us something about that noisiness.
Having now spent some more time reading about classical test theory, that seems to be exactly what it must mean? So I'm not sure what your "No" is in reference to, exactly.
My background is closer to econometrics, you could say, and I find that the various applied fields (psychometrics, econometrics, etc.) tend to organize and relabel the statistical concepts/literature in their own somewhat idiosyncratic ways, and I find it useful for understanding to call out the connections. As in, "ah this is another instance of the errors-in-variables problem, and here's how psychometricians talk about it."
My vague hunch would be that identical twins reared apart tend to often both be raised about the 25th percentile of income. Say, identical twins are orphaned because the parents are killed in a car wreck or the parents both become drug addicts or whatever. So the extended family, maybe both sets of in-laws, gets together and says, "OK, I know this will be a major sacrifice, but we've got to dig deep and figure out who can afford to raise the two kids."
But nobody has the money to take both, so one couple takes one twin and another couple takes the other.
So, there don't seem to be too many Prince and Pauper-style examples of identical twins being raised apart at different ends of the social scale, because if one relative is really rich, she'd probably take both twins.
What’s the correlation for the mother to child and father to child? Is one larger than the other?
Same. See
https://sci-hub.se/10.1126/science.7195071
Sorry if dumb question but, would the same person/same genetic theoretical individual, one raised poor and one raised wealthy, score identically on IQ tests?
Depends on the extent. Poor, as in Africa tier? No. Poor, by America’s standards, probably.
Ah so insofar as poverty may lead to things like malnourishment during childhood it negatively impacts IQ?
It’s a controversial topic, but I support the view that malnutrition does lead to lower IQ as an adult, though empirical tests of the hypothesis have been disappointing.
Illiteracy is probably a big one, too. The harder it is for one to read, the harder it is to maintain a large vocabulary, or review information. The smaller the vocabulary, the harder it is to sharpen one's thinking, understand abstract concepts, communicate ideas, or solve problems.
But I don't see further educational literacy efforts making much difference. There's still only so much you can do when someone's in the 80s and below, so I really do think gene therapy will be the only truly effective means to solve the Third World's low-average-I.Q. problem.
The only problem with this looking at identical twins reared apart is there is still a womb effect. How much of our intelligence is actually shaped by the conditions of the mother's womb having an effect on the brain?
Embryo splitting is done regularly in cows and creates identical twins. In theory one could split a human embryo, implant the resulting identical twin embryo in different moms and compare.
A lot of effort for a study unlike to pass the IRB and given the results above I doubt the womb effect is a big thing unless moms smoke crack.
Do we know to what extent the heritability varies? Is it additive? For example, if the dad is high IQ and the mom is low IQ, are their offspring likely to average out in the middle or inherit either high or low IQ? If both parents are high IQ, do their kids have an increased chance of having an even higher IQ than either parent?
"If both parents are high IQ, do their kids have an increased chance of having an even higher IQ than either parent?"
No. On the contrary the kids are more likely to regress closer to the mean of their ethnic group. But with luck or enough kids it is likely that some will be higher IQ than their parents.
For the less knowledgeable among your readers: I suppose that test reliability is estimated b the correlation when you test the same person twice. Correct?
Internal consistency. Usually with cronbach’s alpha or (better), the omega reliability statistic.
I found some more context on Wikipedia, because this also interested me, being a psychometrics-outsider, as it were. I believe the idea that Hyperdupont refers to would be like using "parallel tests" to estimate reliability ("parallel" because you wouldn't actually want to give the same person the *exact same* test twice with the same questions on it, because they'll remember them; it would have to be a "parallel test" with different questions but the same score expectation and variance).
The Wikipedia article on Classical Test Theory elaborates:
> Using parallel tests to estimate reliability is cumbersome because parallel tests are very hard to come by. In practice the method is rarely used. Instead, researchers use a measure of internal consistency known as Cronbach's α.
> Cronbach's α can be shown to provide a lower bound for reliability under rather mild assumptions. [...] Thus, this method is empirically feasible and, as a result, it is very popular among researchers.
https://en.wikipedia.org/wiki/Classical_test_theory#Evaluating_tests_and_scores:_Reliability
And when you refer to reliability-adjusted correlation, is that like an errors-in-variables adjustment where you use the reliabilities to estimate the measurement error in the predictors?
It’s a little unsatisfying to just assume the .91 reliabilities for so many of the tests, but at least a decent chunk of your N has empirical reliability estimates.
>And when you refer to reliability-adjusted correlation, is that like an errors-in-variables adjustment where you use the reliabilities to estimate the measurement error in the predictors?
No.
My apologies if I've provoked your curtness somehow :(
I was just asking if this:
> The mean correlation is 0.7, mean reliability-adjusted correlation is 0.77...
... referred to disattenuation, i.e., correcting for the dilution that results from considering the individual-level IQ measurements to be noisy variables themselves, enabled by the reliability estimates, which tell us something about that noisiness.
Having now spent some more time reading about classical test theory, that seems to be exactly what it must mean? So I'm not sure what your "No" is in reference to, exactly.
My background is closer to econometrics, you could say, and I find that the various applied fields (psychometrics, econometrics, etc.) tend to organize and relabel the statistical concepts/literature in their own somewhat idiosyncratic ways, and I find it useful for understanding to call out the connections. As in, "ah this is another instance of the errors-in-variables problem, and here's how psychometricians talk about it."