The article "How Religious is Your State?" states that our state, Alabama is the leading religious state. Which means that adults in Alabama attend a religious service at least once a week, pray daily, believe in God, and "say that religion is very important to them". The article says that if an adult follows two out of the four "behaviors" then they are "highly religious". 

I'm not entirely sure why political scientists might be interested in this, but I think it might be because they want to track what religion leans towards which political side, and whether or not religion ties into politics.