Baseline data on occupations were categorized into eight sector-defined occupational groups.
The risks can, in general, be categorized into three groups: operational, occupational, or economic.
The occupational level is categorized into five categories from 1 (low occupation), to 5 (high occupation), following the definition of Statistics Netherlands [ 21].
To assess occupational history, different occupations were categorized into four classes that were derived from the nine classes used by the Italian Statistical Institute [ 64].
Occupational status as an indicator of socio-economic class was categorized into three levels based upon the occupational code [Danish version of the International Standard Classification of Occupation 1988 (ISCO88) of the International Labor Office (ILO, 1990)] using Erikson and Goldthorpe's class categories [ 22].
Men were categorized into the 'low' category if their occupational physical activity was <8 kj/minute, 'intermediate' if they fell into the 8 12 kJ/minute category, and high if their occupational physical activity was >12 kJ/minute.
Patients' occupational status was categorized into six classes: upper-level white-collar workers, lower-level white-collar workers, blue-collar workers, students, pensioners and others (housewives, unemployed), using the classification recommended by Statistics Finland [ 19].
‡ Occupational status is broadly categorized into 3 groups.
Childhood social class was assessed as father's highest attained occupational status and was categorized into three groups using the RGSC: I or II (professionals and managers); III skilled non-manual or III skilled manual; and IV or V (semi-skilled or unskilled occupations).
The mothers' and fathers' socio-occupational status were then categorized into three groups: The 'high' category included women or men in management positions or in jobs requiring higher education, generally more than 4 years beyond high school.
