From http://www.flickr.com/photos/jurvetson/2275614130/
"Definition: Religiosity is measured using a three-item index ranging from 0-3, with 3 representing the maximum religious position. Respondents were given a +1 if they believe faith in God is necessary for morality; and +1 if they say religion is very important in their lives; and +1 if they pray at least once a day."