Inductivist

 Someone at Twitter, I forget now, wondered if IQ or one's social class was more important for adult success. Well, the General Social Survey can help with this. I threw in basic demographics as controls. 

Here are OLS results for income:

Looking at the betas, you can see that IQ is more strongly predictive of income than father's socioeconomic status (PASEI). Notice how race is not statistically significant when IQ is included in the model. 

And job prestige? 

IQ is much more predictive of job prestige than father's PASEI. 

The results for education should be even stronger for IQ:

 

The beta for IQ is much larger than for dad's social class. How far one goes in school depends much more on brains than dad's wallet (or his other influences). 

 In "The Son Also Rises," Gregory Clark presents historical data that suggests that French Americans are an underprivileged minority. They have been underrepresented among doctors and lawyers, for example. 

Do General Social Survey data support this view? 

Here are mean years of schooling for the French versus other white Americans:

No difference in education. Here's median income in 1986 dollars:

A lower median income for Americans of French descent. And mean job prestige:

The French have a slightly higher mean job prestige. And IQ?

Basically the same mean IQ.

Clark predicted to the French would eventually move to average levels. It looks like they've made it.  

 According to conventional economic theory, growing up in a large family predicts less income as an adult because parents were unable to invest as much in each child. By contrast, genetic theory would predict that that family size would not matter for how much income you earn as an adult; rather, income would be predicted by one's IQ. Let's test these two competing hypotheses using General Social Survey data. 

Respondents were asked how much income they earned in the past year, and they were also given a ten-word vocabulary quiz, which makes a decent proxy for IQ (N = 19,902).

This table shows the estimates for a regression model that includes personal income in constant dollars as the dependent variable and the number of siblings as the predictor. You can see that each additional sibling results in a predicted reduction in one's income of $1,139.  (I believe these are 1986 dollars.)

Looking at this table above, we can see that IQ is positively related to income, and the beta indicates that the relationship is of considerable magnitude. It is predicted that each additional IQ point will result in an additional $423 in income. 

The unstandardized coefficient for number of siblings has dropped from $1,139 down to only $586. In other words, much of the reason why a large family predicts a smaller income is due to the correlation between having many siblings and having a lower IQ. This finding supports, to some extent, the genetic hypothesis. On the other hand, we see that the sibling coefficient is still statistically significant, so even after controlling the influence of IQ, the number of siblings is still negatively correlated with income. The economic hypothesis appears to have something to it. 

Evolutionary theory claims that men value physically attractive partners while women desire partners with high status. Normally, we think of status in terms of income, but we can divide men in terms of their sexual success with women. Physical attractiveness is correlated with youth, so I calculated the age difference for married couples. The following is the average number of years that the husband is older than the wife (General Social Survey, sample size = 338):

Mean number of years that the husband is older than the wife by husband's income

Low-income      2.93
Middle-income  2.23
High-income     1.66

This is the opposite of what we predicted: the age gap is smallest for the high-income. Evidently, wealthy men and their wives are more egalitarian, while poor couples are more traditional.

And by number of sex partners since age 18?

Mean number of years that the husband is older than the wife by sex partners since 18

0-3       1.81
4-6       2.86
7-9       2.08
10-19   2.48
20+      4.54

The mean bounces around for the lower numbers, but the men with 20 or more sexual partners have the youngest wives by far.

Sexually successful men seem to be trading their appeal for more youthful wives, but this does not seem to be the case for men with lots of money.

In the last post, it was mentioned that high IQ people are VERY diverse in terms of income. Many are not particularly interested in pursuing lots of money. But let's look at the other end: Few people would want to be poor, so does IQ keep one out of poverty?

Using General Social Survey data, I looked to see how many people in the highest IQ category (125+) are found in the lowest 10% of income earners (sample size = 16,626). For men, it's 3.4%. So smart guys have a low rate of poverty, but not all escape it. I imagine these men have serious physical or mental health issues.

For smart women, it's 8.0%. Their rate is lower than average, but not by that much. In addition to the health issues that men might face, some intelligent woman are likely to be stay-at-home moms who don't earn much.

We know that IQ only has a moderate correlation with income, and it looks like much of this is due to the fact that intelligent people are very diverse in terms of earnings: some are super rich but many aren't very interested in money and pursue other things. I, for example, don't make more than my dad who was a maintenance man and belonged to a union. I could have pursued high-paying business jobs like my brothers, but I was drawn to academics (unfortunately!).

But does the correlation vary with age? Perhaps the earning capacity that comes with IQ becomes more and more evident with the accumulation of years.

Using General Social Survey data, I calculated Pearson correlations between IQ and personal income. Here are the correlations by age group and gender:

Correlation between IQ and income

Men
Ages  18-24  -.03
          25-34   .14
          35-44   .20
          45-54   .26
          55-64   .27

Smart men ages 18 to 24 actually make slightly less than their less intelligent counterparts. Smarter guys are more likely to be in college and thus not earning much money. But we can see the correlation grows with older age groups, and it peaks only in the decade before retirement age.

Women
Ages  18-24   .03
          25-34   .20
          35-44   .20
          45-54   .22
          55-64   .24

We see the same basic trend with women.

These findings are consistent with individual difference research in general: Traits matter more over the long-term and less in any particular situation.

Stefan Molyneux retweeted today the claim that young single women now make more than young single men.  Is that true?

Using General Social Survey (GSS) data, I calculated median incomes for never-married men and women ages 18 to 29 without children who are working full-time.  The numbers shown below are the sex difference between medians, and I include all decades since the 1970s for comparison (sample size = 2,539).  The figures are in constant dollars.

Difference between median male and female incomes 
1970s    1,366
1980s    5,484
1990s       538
2000s    2,625
2010s    6,309

Young men have made more than young women in every decade for five decades, and the biggest gap has been this decade.

The gap is not due to some patriarchal conspiracy (Remind me guys, when and where is the next meeting?) to keep women down. Young men take jobs that make higher wages like construction, while young women are more likely to do something like childcare which doesn't pay crap.

More women are in college, too, so that will make them earn less in the short-term.

The liberal instinctively idealizes and sympathizes with the man at the bottom of society (although liberals are becoming so crazy these days, it's getting hard to characterize them coherently.)  By contrast, a certain brand of conservative might be tempted to idealize the successful man: Effort or perhaps good genes get a guy to the top.

Reality seems a little more complicated than that.  Brains and discipline help a person rise, but so can Machiavellianism.  I suspect that successful people tend to be a mixed bag.

Let's test the idea that there is moral virtue in successful people by looking at marital infidelity.  I divided personal income into 5 levels and created graphs for white and black men (sample sizes = 7,959 and 894):

Black Men
















White Men















Among black males, you see a spike in cheating among the highest income group.  It's a smaller increase among high-earning white males.

So successful men are a little more likely to be unfaithful. You might attribute this to the greater attractiveness that comes with money or to greater social opportunities, but whatever the case, there is no indication here that successful men are more moral than others.  It's important that we stick to reality and not ideology.

There was an Twitter dust-up recently when Nassim Nicholas Taleb used his statistical skills to trash IQ studies.  Two of his criticisms -- if I understand him correctly (he doesn't write so regular folks can understand because he is an elitist) -- are that: 1) IQ only does a good job distinguishing the mentally challenged from those in the normal range of intelligence; and 2) IQ becomes particularly useless at predicting important outcomes (like income) at the high end of the distribution.

I looked at the relationship between the General Social Survey's simple measure of IQ -- a vocabulary quiz -- and the respondent's household income in 1986 dollars. The vocabulary score is the number correct out of 10 questions (sample size = 27,530):
















According to GSS data, Taleb is wrong on his first point and half wrong on his second. See how IQ does not predict income much at all for the lowest four IQ levels.

But it does do a pretty good job of predicting income from levels 3 through 10. Within this range, there is a straight, stair-step increase in income as one moves up in IQ.  This linear relationship does not fade or disappear at the highest levels of intelligence, as Taleb says it does.

On the other hand, the data support Taleb on one important point (you can't see the following on the graph): the problem of heteroscedasticity (unequal variance). For each IQ level from 0 to 4, the variance in income is not high. For example, people at the 0 level do not vary from each other much in terms of income: they're generally pretty poor. Once you reach level 5, people start to diversify more: people are increasingly all over the map in terms of income. And this tendency increases through level 10--the level with the greatest dispersion in income. In other words, while the smartest people have the highest average income, it is a very diverse class of people. Some earns tons of money, others not much.

So, a high IQ seems almost necessary to earn a big income, but it is far from guaranteeing it. 

UPDATE:  The data reminds me that income -- in the US, at least -- is hard to predict because there is so much variation.  Liberals like to refer to it as inequality.  Probably no variable predicts income with a great deal of precision simply because people are all over the map in terms of how much they make.  Taleb takes advantage of that fact when he criticizes IQ.

I wondered which factor most strongly predicts men having sex frequently: youth, money, looks, or being married?  Here are the statistical results (GSS data, sample size = 685 men, standardized OLS coefficients, all effects stat. sig.):

Factors predicting frequent sex

Youth  .32
Income  .14
Good looks  .09
Being married  .16  

Being young is by far the most important factor.  Older guys don't have sex nearly as much.  Next in importance is being married.  I imagine many men think you get more sex when you're unattached.  You might get more variety, but not more sex.  A big paycheck comes in third, but good looks is least important for men.

So if you like lots of sex, don't get old.

A good income is associated with positive characteristics like industriousness and intelligence, traits that are strongly influenced by genes.  High-income adults are obviously in the best position to have large families.  Do they?  Look at the graph (General Social Survey, 2010-2016, women ages 40-55, household income in 1986 dollars, N = 1,325):
















While women with two children have higher incomes than those with no children, income tends to fall as family size increases beyond two kids.  Compared to families with eight or more kids, two-child families earn more than double the household income.

Here's the graph for men ages 45-60 (N = 1,170):
















We see a similar pattern for men, although the income drop beyond two kids is perhaps not as steep as for women. (Don't make much of the high bar for men with seven kids: it's based on only four cases.)

We're seeing the same kind of pattern again and again: Americans who are in the best position to have a big family are least likely to do so.

With these trends, the long-term future will go to the people on the bottom of American society -- the people who have the least genetic potential.

Here's a DHS report of the number of U.S. naturalizations in 2011. I've listed below the top twenty sending countries. Next to the country, I show the median personal income for people born in the U.S. between the ages of 25 and 64 whose family came from the respective country (ACS data) . The overall median American income is $45,149.

Median personal income
1. Mexico 29,076
2. India 50,000
3. Philippines 39,460
4. China 51,921
5. Colombia 38,422
6. Cuba 40,000
7. Vietnam 39,910
8. Dominican Republic 30,000
9. Jamaica 30,969
10. Haiti 32,036
11. El Salvador 30,000
12. S. Korea 41,701
13. Pakistan 41,537
14. Peru 38,000
15. Brazil 39,460
16. Nigeria 34,300
17. Canada 37,376
18. Iran 41,537
19. United Kingdom 45,559
20. Poland 41,537

People from Mexico dwarf all other countries in numbers of 2011 U.S. naturalized citizens (95,000 Mexicans vs. 46,000 Indians--the next largest group) but the median income of Mexican-Americans is only a fraction of the average. It is the poorest group on the list, even lower than black groups. But the news is worse than that. Of the 20 countries listed, only Asian Indians, Chinese, and those whose families came from the UK earn above-average incomes. Americans with ancestors from the other 17 countries are below-average. And Dominicans, Jamaicans, Haitians, Salvadorans, and Nigerians are really low. Immigration from these countries is leading to more low-income Americans. And I'm focusing on native-born Americans, not their immigrant parents. (The reality is probably a little better since the average age of the native-born of many of these groups is lower than the overall American average, and income, of course, is related to age.)

The only bright spot is that two of the large immigration groups--Indians and Chinese--earn a lot of money.

Back to the bad news: not only do the poor groups tend to vote Democrat, their better off members do too, and even wealthy immigrant groups like Indian and Chinese Americans lean Left.

These two Pew graphs show how young women are now more ambitious than men. Sixty-six percent of females ages 18 to 34 say career success is "one of the most important things" or very important" in their lives. The corresponding figure for young men (seen below) is only 59 percent.


I expect this new gap will further weaken the institution of marriage. I'm not sure if the Girl Power crowd is aware of this consequence. Radical feminists, of course, are cheerleading the decline. If a man does not earn more than a woman, he is less attractive as a partner. Most women want a husband, but they are less likely to enter marriage and are quicker to exit it if the man offers fewer positives. Marriage is still comparatively strong among high status people, but economic incentives matter.

This is a structural equation model of a cohort of Swedish men. It shows that IQ is an important determinant of income and especially occupational position.  Much of its influence is indirect: it is a strong predictor of educational level which, in turn, is a powerful determinant of both income and especially occupational position. Parent's social class, by contrast, is comparatively less important. It has little to no direct influence on income or job position, and predicts educational level only moderately.

A whole academic field--sociology--developed on the view that social class is of critical importance. If disciplines emerged as a result of empirical support, students could major in IQiology.

In the comments section of the last post, reader SFG wonders about the characteristics of people who are smart but who do not go to college.

Using GSS data, I created a two-category variable where people with eight through ten out of ten questions correct on a vocabulary quiz but who never went to college are assigned a one, and everyone else is given a zero. Those in the first category make up about 11 percent of the total adult population surveyed over the past 40 years.

Next, I chose eight variables as predictors. Here are the logistic regression coefficients (sample size = 16,215):

Logistic Regression Coefficients

Year -.02
Age .02
Sex .42
Race 1.45
Father's education .03
Church attendance -.04
Political conservatism .01
Number of offspring -.03

All of the predictors are significantly related to the outcome variable except for political conservatism. So what is the profile of someone who is smart but went no further than high school?  I'll attempt to list factors from most powerful to least: older, white, being surveyed in earlier years, female, having an educated father, going to church less often, and having fewer children.

I also compared the mean incomes of the two categories. The smart group that didn't go to college made about $1,000 more a year than the average for the other group.

Many of the factors make sense. Older people from earlier cohorts were less likely to go to college, even if they were intelligent. The same for women. Blacks are much less likely to be bright people who fail to attend college. Having a successful father can sometimes open a good career path that requires no higher education. Perhaps irreligiosity indicates unconventionality. Political attitudes appear to have no effect on choosing to avoid college.

Which factor reduces family size the most? Below are the standardized OLS regression coefficients for a sample of whites ages 40-59:

Standardized OLS regression coefficients

Education -.23*
Income .10*
IQ .00
Church attendance .10*
Belief in God .06*
Political conservatism .06*

*p < .05, two-tail test

Education reduces fertility more than any factor. IQ has no net impact. Look at how income has a significant positive effect on family size. Not surprisingly, religiosity and conservatism are associated with more children.

You don't have to agree with everything Pat Buchanan writes to acknowledge that he's a rare instance these days of a man in the mainstream media with balls. (And Ann Coulter, of course):

The assumption of the Jarrett-backed law is that the sexes are equal in capacity, aptitude, drive and interest, and if there is a disparity in pay, only bigotry can explain it.

But are there not other, simpler answers for why women earn less?

Perhaps half of American women leave the job market during their lives, sometimes for decades, to raise children, which puts them behind men who never leave the workforce. Women gravitate to teaching, nursing, secretarial and service work, which pay less than jobs where men predominate: mining, manufacturing, construction and the military.

Over 95 percent of our 40,000 dead and wounded from Afghanistan and Iraq were men. Men in prison outnumber women 10 to one. Is that the result of sex discrimination?

Sports have become a national obsession, and among the most rewarded professions in fame and fortune. And TV viewers prefer to watch male athletes compete in baseball, basketball, football, hockey, golf, tennis and boxing.

Is unequal pay for men and women professional athletes a matter for the government?

Larry Summers lost his job as president of Harvard for suggesting that women have less aptitude for higher math and that may explain why they are underrepresented on Ivy League faculties in the sciences, economics and math. Would not that male aptitude help explain why men are dominant in investment banking and corporate finance, where salaries are among the highest?

Americans are taught to judge people individually, and in situations where you can get to know someone, this makes sense. But the truth is that you can predict aggregates better than individuals.

Using General Social Survey data, I calculated the correlation between a measure of IQ (WORDSUM) and income (REALINC) for almost 17,000 people born in the U.S.  It turned out to be .28. If you square that number, you get .08 which is called R-squared. It is interpreted as the proportion of variation in income that can be explained by your IQ. In other words, if I know one thing about a person--his IQ square--I am not going to be able to predict his income level with any accuracy at all.

But the situation changes dramatically if I calculate mean IQs and mean incomes for the 29 ethnic groups which have at least 30 respondents in each group. Now the correlation jumps all the way up to .77. If we square that, we get .59, which means that 59 percent of the variation in mean income is explained by the variation in mean IQ scores. So if I've got a random group of, say, Americans of Russian descent, chances are their average IQ is high, and I can make a pretty good bet that the group will earn an above-average income as well.

This is why Richard Lynn and Tatu Vanhanen's approach is so effective in IQ and the Wealth of Nations.  You grab a random guy in Japan, he might be smart or dumb; he might be rich or poor. But tell me the mean IQ of the country is 106, and I'm putting my money on it being a wealthy place.

HBD-ers are criticized for focusing on groups, but reality is most predictable at that level, and being scientific is being concerned with prediction.  

Does atheism make a person wealthier? Atheism might be associated with higher or lower income. Religious folks, for example, might network more which might translate into better money-making opportunites. On the other hand, non-believers might earn more for some reason. Perhaps they see more clearly how one achieves Y and are less encumbered with irrational thinking. Maybe belief and income are unrelated. Myself, I suspect skeptics make a little more because they tend to be smarter.

The GSS asked white Americans about their income and belief in God. I regressed personal income on belief and added Wordsum as a control:


OLS Regression Coefficients (Betas), N = 587

Atheist -.05
Agnostic .07
Believes in higher power -.02
Believes sometimes -.05
Believes but sometimes doubts .08
IQ .18**

** p < .01, two-tail test

The five belief variables are dummies, and the reference category is those who know there is a God. Before IQ is entered into the model, agnostics and believers who sometimes doubt earn significantly more than those who have no doubts. But as you see above, there is no significant assocation between belief and income once IQ is controlled.

So, agnostics and believers with doubts make more, but only because they are, on average, smarter. Atheists do not have higher incomes, even at the bivariate level. This, in spite of the fact that they are more intelligent. Maybe the networking does pay off. Or perhaps disbelief is associated with other characteristics that work against economic success: lack of social skills, for example.

Promiscuity and getting a lower-earning husband: Few women seem to read this blog, so I might be talking to myself, but if you want to marry a man who earns more than you, then don't be a slut. Here is the mean number of lifetime sexual partners since age 18 by who has a higher income:


Mean lifetime sexual partners (GSS women, N = 327)

They have the same income 3.24
Spouse has no income 3.65
Husband has a higher income 3.75
Husband has a much higher income 3.80

All wives 4.17

Wife has a much higher income 6.38
Wife has a higher income 7.33

With the exception of the unusual situation of having a husband with no income, women with fewer partners end up with wealthier men. Women who end up with low-earning men were almost twice as promiscuous. More masculine women might explain the correlation, but men are still old-fashioned enough to not want to marry the town whore.

(It might also be the case that women who wait longer to get married because they are building careers may pick up more sex partners along the way, but I still like my interpretation.)