The GPPAQ generates a four-level Physical Activity Index (PAI), which allows subjects to be categorized into active, moderately active, moderately inactive and inactive groups. To enable statistical analysis we labelled the groups with nominal values of 4, 3, 2 and 1, respectively. The number of exercise days per week was also recorded (defined as days when the level of physical activity conducted would lead to a subject breathing more deeply or harder than usual and which would result in difficulty talking).