If I compare dogs in one area with dogs in another area, it doesnt really matter what cats are doing.
But the point of the study is: Conservative protestants are more likely to get divorced. But that is because they are also more likely to get married. So whether they include shack ups or not in the study is really an issue (although it would be intersting since the left is always trying to redefine marriage). But the study is clearly flawed, and it's conclusion is foregone due to the methodology.
See #18 and #23....bolobaby makes a very good point.
I believe the results would be the same if compared between Conservative Protestants and Conservative Catholics.