Just one note: I realize the post isn't copiously referenced -- most of them come from the refs in the Matthews, Deary, & Whiteman book, or simple Pub-Medding. I'd go to the relevant section of Personality Traits, which is searchable at Amazon (and cheap in paperback), or Pubmed "cortical arousal extraversion" for example. I wanted more links, but this has been a back-burner post for awhile, and I wanted to get it out sooner rather than never.

Reading Judith Rich Harris' "No Two Alike" got me to wondering how reproducible are personality measurements. I recall IQ test scores correlate (test-retest) at about 80%. Using google scholar I dug up some articles on correlation (test-retest) for personality tests. I was surprised to see the dominant eigenvector (introversion) reliable at the 80% level, with other eigenvectors diminishing towards about 50% for the fifth eigenvector. All much better than I (an engineer) would have guessed.

Agnostic, good post. I look forward to part 2.

Jon -- not only do short-term test-retest reliability coefficients range from 0.7 to 0.9 (excellent for psychometric measurement), but if you test someone now and 10 years from now, they won't have changed much. The longer-term correlation will be somewhat lower, but when you take the disattenuated correlation, they go upwards of 0.9, indicating that the weakened correlation between now and 10 years hence is mostly an error of measurement, not a real change in one's personality traits. (Data & refs in Personality in Adulthood by McCrae & Costa; search index for "retest reliability.")

Such little change over time is true for crystallized and verbal IQ tests, but not for the more fluid and visuospatial ones like Ravens, the scores on which tend to deteriorate over time, esp. after ~50 (see Looking Down on Human Intelligence by Deary, Ch. 8). So in a sense, personality traits are more enduring aspects of a person's being than reasoning abilities. Not too surprising, as intelligence is more of a skill like athleticism while personality is like a set of strategies. Natural selection may not have cared much if 60-y.o.s could perform pattern recognition like they could in their 20s, but anyone will still need to navigate social and personal life.

More praise, and encouragement for part2. Nice work distilling the unifying skeleton of such disparates.

What's your opinion on the Myers-Briggs system of personality typing? I know the Big-5 test is more fashionable among psychologists, but I think the Myers-Briggs test works pretty well for a four-factor model. Also, the Myers-Briggs system seems to emphasize that there are inherent trade-offs in having one personality type over another, whereas the Big-5 system makes more of a value judgment (obviously openness, conscientiousness, and agreeableness are better than their alternatives).