Let's begin with income. If one assumes that people with more money are more likely to travel overseas, one would be absolutely correct.





There is a considerable correlation between passports and both median income (.81) and per capita economic output (.70). No matter how you slice it, wealthier states have more passport holders.

It's also reasonable to assume that more highly educated people would be more likely to hold a passport. And that too is what we find across the states. There is a considerable correlation (.80) between passports and human capital levels (measured as the percentage of a population with a bachelor's degree or higher). What's really striking is that this correlation holds even when we control for income, using a statistical procedure called partial correlation analysis.

Passport holding also reflects the structure of state economies. There is a substantial correlation (.70) between the percentage of passport holders and the percentage of the workforce in knowledge-based and creative jobs. Conversely, there is significant negative correlation between passport holders and the share of the workforce in blue-collar working class jobs (-.82). Working class states have considerably less passport holders than creative class states. Again, the correlations hold when we control for income.

States with higher percentages of passport holders are also more diverse. There is a considerable correlation between passports and the share of immigrants or foreign-born population (.63) and also gays and lesbians (.54). The more passport holders a state has, the more diverse its population tends to be. And yes, these correlations hold when we control for income.

What about politics? How does passport holding line up against America's Red state-Blue state divide? Pretty darn well, actually. There is a considerable positive correlation between passports and Obama voters (.59) and a significant negative one (-.61) for McCain voters. It appears that more liberally-oriented states are more globally oriented as well, or at least their citizens like to travel abroad. Again, the correlations hold when we control for income, though they are a bit weaker than the others.

Passport holding also reflects something about the underlying personality of places. American states are not only sorting by income, education and political orientation, but by personality type, according to research by the Cambridge University psychologist Jason Rentfrow and his colleagues. Passport holding is in fact related to three of the five major personality types. There are positive correlations between passports and Openness-to-Experience personalities, and negative ones to both Agreeableness and Conscientiousness. "The results suggest to me that this is also linked to Openness," Rentfrow noted after looking over these findings. "Openness is about curiosity and adventure, so it would make sense that Open places have high numbers of passports."



And finally, states with more passport holders are also happier. There is a significant correlation (.55) between happiness (measured via Gallup surveys) and a state's percentage of passport holders. Yet again, that correlation holds when we control for income.