Cause or effect? Do people learn to join in caucus states? Or is it just something in the water?

"...Primaries draw a very different type of voter than a caucus does. In a paper on this topic, Eitan Hersh shows that primary voters and caucus-goers aren't necessarily different ideologically—caucus-goers aren't more extreme or less tolerant—but they do differ on other dimensions, specifically political engagement. Caucus-goers are joiners. They're more likely to attend meetings and join organizations than primary voters are."

http://www.psmag.com/politics-and-law/what-states-get-when-they-decide-to-hold-a-primary-instead-of-a-caucus-and-why-it-matters-so-much