The variables that were used were: sex, grade, pain (how often a week), physical activity (light/vigorous) and physical inactivity (sedentary for <2/> 3 hours).
Breyturnar sem notast var við voru; kyn, bekkjarárgangur, verkur (hversu oft í viku), hreyfing (létt/mikil) og hreyfingarleysi (kyrrseta í <2/> 3 tíma).