Sub-scores for physical activity and work are calculated, with 7 items assessing beliefs about work (item 6, 7, 9, 10, 11, 12, 15) and 4 items assessing beliefs about physical activity (item 2, 3, 4, 5).
Furthermore, an EDY-Q mean score was calculated with all items except for the two items on the exclusion criteria.
Pearson correlation was calculated with other items as the independent variable.
First, when the PAM is used as a guide for triaging individuals to a specific level or type of an intervention, PAM scores calculated with missing items must be considered with caution.
An index of SES was calculated with the items that referred to the parents' education and parental occupation classifying SES as: lower, lower middle, middle, upper middle, and upper according to the scale proposed by the Spanish Society of Epidemiology [ 16].
No correlations were calculated with the item number of events reported, because of the lack of variability and skewed nature of this item (90% of the respondents indicated not to have reported any incidents during the last twelve months).
To provide composite scale scores average scores were calculated with each item assigned equal weight (Cronbach's alpha = 0.80).
Relevant models of probabilistic test theory (De Ayala 2009), therefore, were calculated with generalized Item Response Modelling Software (Acer´s ConQuest 2.0; Wu et al. 2007).
Alphas were also calculated with each item deleted.
Cronbach's alpha was calculated with each item removed in turn.
