Political Affiliation and Opinions on the Designated Hitter Rule
David Pinto links to a paper studying the relationship between political affiliation and opinion of the designated hitter rule in Major League Baseball. It's an interesting paper, and the reasoning behind the findings (Democrats favor the DH more than Republicans do) seems sound.
But I think a big failing of the study is in its weak modeling of the effect of a fan's support of a particular team. The only data the researchers had available was the state of residency of each respondent. Dummy variables were then applied based on whether or not the respondent lived in a state with an NL or AL team. Unfortunately, that means that residents of California, Texas, Illinois, Missouri, Florida, Ohio, and New York* were assigned both dummy variables and we don't have anything more detailed on whether someone from Illinois is, say, a Cubs fan or a White Sox fan (much less a Cards fan, etc.)
Similarly, all of California is lumped into one catch-all category, so we can't see how the difference plays out between the NL Dodger fans from more liberal Los Angeles and the AL Angel fans from more conservative Orange County (or, for that matter, Padre fans from conservative San Diego).
Obviously, you can only work with the data you have, but even if all you know of a respondent is the state they live in, you can get a more thorough understanding of the relationship between that geography and fandom at this Common Census map of the results of a survey on geography and team affiliation. Based on this map, I would say that one could safely assign all of New England to the American League (due to the Red Sox and, to a lesser extent, the Yankees), and a wide swath of the South from Mississippi to the Carolinas can safely be considered Atlanta Braves territory.
Be careful not to make too much of the fact that the Yankees dominate most of New York State's area and that Illinois appears to be split between two National League teams, the Cubs and the Cardinals. The Mets and White Sox may only dominate very small areas, but the areas where they are popular are densely populated and thus their fans form a much more significant fraction of the overall fanbase within their home state than would appear just from looking at the colors on the map. Also note that the two teams that have the most number of "expatriate" fans away from their home city are both in the AL, the Yankees and Red Sox.
Incidentally, I'm a Democrat, a fan of a National League team (the Dodgers, of course), and am opposed to the Designated Hitter rule.
*The researchers don't mention Texas, but I assume this was an oversight in the writeup. Not coincidentally, these seven states with both AL and NL teams all have large populations, together accounting for 42.3% of the country's total.