With regard to yesterday's question about whether the "marriage gap" stands up to more sophisticated statistical scrutiny, Steve Sailer recommends his article "Values Voters" in the current American Conservative which, in turn, cites "Unmarried Women in the 2004 Presidential Election" by Anna Greenberg and Jennifer Berktold which finds:
The marriage gap is a defining dynamic in today’s politics, eclipsing the gender gap, with marital status a significant predictor of the vote, independent of the effects of age, race, income, education or gender. Marital status had a significant
effect on the way in which these voters performed, whereas a voter’s gender did not. This was true of all age groups. Younger unmarried women supported Kerry while younger married women supported President Bush. Unmarried 18- 29 year olds gave Kerry a 25 point margin, while younger married women, like their older counterparts, gave President Bush an 11 point margin.
As you can see over on the left, this suggests that the hypothesis that unmarrieds vote Democratic because the unmarried population skews younger and young people support Democrats is wrong. On the contrary, being 18-29 seemed to have a weak independent correlation with voting for Bush while being unmarried had a strong correlation with voting for Kerry. Thus, that hypothesis actually has it backwards and suggests that Kerry had an advantage with the 18-29 crowd in large part because it contains so many single people.
It does seem worth saying, however, that "unmarried" is an awful heterogenous situation. Of course, any binary categorization is going to produce diverse groups of people in both categories. But in particular treating divorced people and never-married people as part of the same category seems like the kind of thing that could easily create misleading results.