Inductivist

The Multidimensional Personality Questionnaire (MPQ) is an alternative to the Big 5. In the analyses that I have conducted, MPQ traits have been more predictive of outcomes than the Big 5. I calculated means for atheists, agnostics, those with no religious preference, and all others (sample size = 3,946). 

Mean MPQ scores

Well-being
No religious preference 8.76
Atheist 9.07
Agnostic 9.13
Others 8.99

Social Potency (likes to take charge)
No religious preference 10.29
Atheist 10.73
Agnostic 10.60
Others 10.20

Achievement
No religious preference 12.18
Atheist 12.61 
Agnostic 12.35
Others 12.25

Social Closeness (likes to be with others)
No religious preference 11.03*
Atheist 10.71*
Agnostic 10.32*
Others 11.94

Reactivity (easily upset)
No religious preference 6.30
Atheist 5.17*
Agnostic 6.62
Others 6.19

Aggression (confrontational)
No religious preference 5.74*
Atheist 5.40
Agnostic 5.53
Others 5.38

Alienation (life is unfair to me)
No religious preference 5.21
Atheist 4.21*
Agnostic 4.72
Others 5.14

Control (plans before acting)
No religious preference 9.45*
Atheist 9.56
Agnostic 9.47
Others 9.79

Traditionalism
No religious preference 6.75*
Atheist 4.88*
Agnostic 5.53*
Others 8.66

Harm avoidance
No religious preference 11.57*
Atheist 9.93*
Agnostic 11.07*
Others 12.13

*significantly different from "Others" group


Compared to people who have a religion, those with no preference are significantly less social, more confrontational, less planful, much less traditional, and more danger-seeking. The image that emerges here is a lone rebel.

Turning to atheists, they are less social, less likely to get upset, less likely to think life is unfair to them, much less traditional, and more danger-seeking. Atheists seem like a milder version of those with no preference: solitary, danger-seeking, anti-traditionals who are not confrontational, who plan ahead, and who don't think the world has given them a raw deal. 

Agnostics are less social, less traditional, and more danger-seeking. All three non-religious categories have three traits is common: they don't like people as well; they really dislike tradition and authority; and they like risk more than others.

I don't see any necessary connection between disbelief and anti-traditionalism--I certainly did not dislike religion or tradition when I was a skeptic--but they are psychologically like oil and water.

Readers SFG and HBD Chick suggested that I compare the personality traits of agnostics with non-agnostics (MIDUS data, sample size = 3,960).


Mean scores

Extraversion
Agnostics 2.82*
Others 3.10
Cohen's d .49

Negative emotionality
Agnostics 2.15
Others 2.09

Agreeableness
Agnostics 3.23*
Others 3.45
Cohen's d .44

Conscientiousness
Agnostics 3.36*
Others 3.49
Cohen's d .29

Openness to experience
Agnostics 3.17*
Others 2.90
Cohen's d .50

*Agnostics and others are significantly different

Compared to the general population, agnostics are more introverted, less agreeable, less conscientious, and more open. They are like atheists, only shy and neurotic.

General Social Survey respondents were asked: "Do you agree or disagree that life does not serve any purpose." Answers ranged from "strongly agree" (5) to "strongly disagree" (1). Here are the means by belief in God:


Mean nihilism score (N = 3,708)

Does not believe in God 1.68
There is no way to find out 1.75*
There is some higher power 1.72*
Believes sometimes 1.89*
Believes but doubts 1.62*
Knows there is a God 1.48

*significantly more nihilistic than those who know there is a God


All of the groups except atheists are significantly more nihilistic than those who know there is a God. (The sample size for the atheists is small).  The largest gap, that between knowers and those who believe sometimes, is half of a standard deviation--a fairly large difference.