Inductivist

This study of Senegalese men from the December 2010 issue of Personality and Individual Differences shows that extraversion predicts mating effort and that extraverted men have higher levels of testosterone. By contrast, other Big 5 personality traits (i.e., neuroticism, openness and agreeableness) are unrelated to mating effort and testosterone levels. It looks like the dominance component of extraversion--linked in other studies to testosterone--is crucial.

Extraversion and political influence: Based on IQ, one would expect Jewish Americans and Asian Americans to have a disproportionate political influence on the country. We certainly see this with Jews, but not Asians (correct me if I'm wrong). Based on IQ levels, we would not expect blacks and Hispanics to have much influence, but of the two, Hispanics should be more powerful since they are smarter. The truth, though, is that blacks are the stronger group.

My recent posts might help explain this pattern. Blacks and especially Jews are extraverted groups, Asians and Hispanics are not. American Indians are another introverted group who seem to be practically invisible. Of course, population is a factor with all the groups, and I'm not arguing that groups do not have power on particular issues. I'm thinking more of an overall presence in the political process.

IQ and extraversion might also explain the disproportionate influence of homosexuals. My last post revealed that homosexuals and bisexuals have high extraversion scores, and I showed some time ago that the mean IQ for white gay men is 105.

Extraversion can also help explain differences in cultural influence and media presence.

And let's not forget that broad heritability for extraversion is around .5, suggesting that genetic differences might help explain these patterns.

Homosexuals and bisexuals are more extraverted: Here are mean introversion scores (GSS behavioral measure--self-reported trait not available) for sexual orientation groups:


Mean introversion score (N = 11,642)

Straight women 14.2
Straight men 13.4
Lesbians 13.2
Gay men 12.2
Bisexual men 11.7
Bisexual women 11.0


All groups are significantly more extraverted than straight women (p < .05. two-tail). N's are pretty good. The smallest group is bisexual men at 35. Here are the effect sizes:


Effect Size

Straight men .22
Lesbians .28
Gay men .56
Bisexual men .69
Bisexual women .89

The differences between straight men and lesbians on the one hand and straight women on the other are small, but the straight women/gay men difference is of moderate size. Bisexuals of both sexes are much more extraverted than heterosexual women.

The Extraversion Gap: In an earlier post, I used a behavioral measure to show that Jewish Americans are, on average, more extraverted than Americans of English descent. The finding is reinforced by my other GSS measure of extraversion based on two questions asking if you are: 1) sociable and 2) not reserved. The means are:


Mean extraversion score

English 6.44 (n = 122)
Jewish 7.35 (n = 26)

Since the Jewish sample is so small, the difference falls just short of statistical significance at the .05 level. The effect size is .54 which indicates a half standard deviation gap between the two groups.

Extraversion and lifetime sex partners: Here are the median lifetime sexual partners for different demographic groups ages 30-59 by level of extraversion:


Extraverts
White men 8.0
Black men 10.0
White women 4.0
Black women 3.0


Introverts
White men 5.0
Black men 10.0
White women 3.0
Black women 3.0


Extraversion is associated with more partners for both white men and women, but not for blacks. It seems odd that introverted black men have the same median partners as extraverted black men.

And you can see the typical gender disparity: men are probably exaggerating while women are under-reporting their sexual experience. (Prostitutes probably up the male numbers as well). The gender gap is larger for blacks.

Extraversion and type of job: I put together a list of the mean introversion scores of people in various occupations. I included them if they were significantly higher than average ("introverts") and if they were significantly lower ("extraverts"). The sample size is 16,796 (GSS).


Introverts

Mail clerks, except postal service 16.3
Laundering and dry cleaning machine operators 16.0
Postal clerks, except mail carriers 15.9
Statistical clerks 15.7
Licensed practical nurses 15.7
Typists 15.6
Private household cleaners and servants 15.5
Farmers, except horticultural 15.4
Textile sewing machine operators 15.4
Farm workers 15.3
Maids and housemen 15.3
Librarians 15.3
Bus drivers 15.1
Hand packers and packagers 15.1
Laborers, except construction 15.1
Machine operators, n.s. 15.1
Cooks, except short order 14.9
Assemblers 14.9
Nursing aides, orderlies, and attendants 14.8
Bookkeeping, accounting, and auditing clerks 14.7
Janitors and cleaners 14.7
Registered nurses 14.5
Secretaries 14.3


Extraverts

Designer 13.2
Managers, properties and real estate 13.1
Real estate sales occupations 13.1
Painters, sculptors, craft-artists, and artist printmakers 13.0
Sales occupations, other business services 12.9
Advertising and related sales occupations 12.5
Actors and directors 12.4
Airplane pilots and navigators 12.1
Architects 11.8
Athletes 11.7
Securities and financial services sales occupations 11.4


I don't see any big surprises. Introverts tend to have clerical or low-skill jobs, while extraverts have jobs requiring people skills (sales), leadership skills (managers), or creativity (designers, artists, actors).

Growing introversion: Here are America's mean introversion scores over four decades:


Mean introversion score

Seventies 13.8
Eighties 14.0
Nineties 14.1
This decade 14.2*

* p < .05, two-tail test, compared with the seventies


The country has gradually gotten a bit more introverted. This might be due to increasing numbers of Asians and Hispanics. (Immigrants in general tend to be more introverted).

English Americans are most introverted, Jewish Americans are least: Here are mean introversion scores for various white American groups:


Mean introversion score (N = more than 20,000)

English/Welsh 14.2
Dutch 14.2
Swiss 14.2
Scottish 14.0

All ethnicities 14.0*

Irish 13.9*
Hungarian 13.9
Portuguese 13.9
Spain 13.9*
German 13.8*
Danish 13.7*
Rumanian 13.7
Polish 13.6*
Swedish 13.6*
Belgian 13.6
Italian 13.5*
Czech 13.5*
Russian 13.4*
Norwegian 13.4*
French 13.4*
Yugoslavian 13.4
Finnish 13.3*
Lithuanian 13.3*
Jewish 13.3*

* p < .05, two-tail test, compared with English/Welsh


The groups with asterisks are significantly more extraverted than Americans of English or Welsh descent. Here are the effect sizes for those who differ significantly:


Effect size

Irish .09
Spain .09
German .11
Danish .14
Polish .17
Swedish .17
Italian .20
Czech .20
Russian .23
Norwegian .23
French .23
Finnish .26
Lithuanian .26
Jewish .26


The differences among whites groups, even at the extremes, are small.

I checked to see if the observed pattern was influenced by immigration. I suspected that immigrants are more introverted than natives, and I was right. If we compare Jews and those of English descent born in America, the effect size increases to .37--a moderate difference.

Extraversion and number of offspring: As a follow-up to the last post, I looked to see if introverted people have more children (GSS data, N = 10,153). For people ages 40-59, the correlation between introversion score and number of offspring for each of the past four decades has hovered around .10. A trivial positive association.

Extraversion and marital status: Here are the mean introversion scores for each marital status for Americans ages 30-49 (GSS data):


Mean introversion scores (N = 2,870)

Married 14.6
Widowed 14.3
Divorced 13.5*
Separated 13.7*
Never married 13.0*

* p < .05, two-tail test, compared with married people


All groups except for widowed are significantly more extraverted than married people. Makes sense. Marriage is for homebodies. Introversion might help explain the lower divorce rate of Asians. Here are effect sizes:


Effect size

Divorced .32
Separated .25
Never married .46


The differences between married/widowed people and the other categories are small to moderate.

Race, extraversion, and crime: Using last post's measure of extraversion, I wonder if it could help explain racial differences in crime. Ever getting arrested is the dependent variable. Here are the logistic regression coefficients, and I'm comparing two groups at a time:


Logistic regression coefficients

Whites and Asians (N = 3,087)

White 0.64
Extraversion 0.14*


Blacks and Asians (N = 468)

Black 1.46
Extraversion 0.12*

* p < .01, two-tail test


Compared to Asians, whites are more likely to get arrested, but the difference becomes non-significant when extraversion is entered into the equation. The exact same thing happens when we compare blacks and Asians. So the evidence here suggests that extraversion helps explain the racial gap in criminality.

But why, you ask, would extraversion raise the risk of breaking the law? Compared to, say, the guy who likes to spend his time blogging alone, people who love to be out doing things with other people are more likely to find themselves in situations conducive to crime. And they would be less likely to back away from criminal opportunities.

Another look at extraversion: I took another approach to measuring racial and ethnic differences in extraversion by looking for GSS behavioral questions. Respondents were asked how often they: 1) visit neighbors, 2) visit friends outside of the neighborhood, and 3) go to a bar. Answers varied from "almost every night" (1) to "never" (7).

These items were all positively correlated with each other, but Cronbach's alpha is only .45. I summed them together to create an introversion score and limited the analysis to those ages 30-49 out of concern that the groups might have different average ages and that going out, especially to bars, is influenced by age. Fortunately, the sample size is large (N = 9,528).


Introversion score

White 13.80
Black 13.91
Mexican 14.84*
Chinese 14.79*
Filipino 14.57
American Indian 15.04*

*p < .05, two-tail test, compared with whites.


Consistent with the earlier analysis, blacks and white do not differ, but Mexican Americans are significantly more introverted. The large sample size allowed me to look at other minority groups, and you can see that Chinese Americans and American Indians are less outgoing. The difference between whites and Filipinos fell just short of statistical significance. I went ahead and calculated the effect sizes too:


Effect size

Mexican .30
Chinese .29
Filipino .22
American Indian .36


These numbers indicate small to moderate ethnic/racial differences. Keep in mind that broad heritability for extraversion is around 0.5.