Table 1.

Dichotomization of the categorical variables

Variable	Answers coded as ‘1’	Answers coded as ‘0’
Seeking medical advice because of spinal pain School absenteeism because of spinal pain Sport absenteeism because of spinal pain	‘once in a while’ ‘often’	‘never’ ‘once or twice’
Self-rated health	‘excellent’ ‘very good’	‘good’ ‘fair’ ‘poor’
Impact of spinal pain on self-rated health	‘my health would be clearly better without spinal pain’	‘no impact as I have no pain’ ‘no impact’ ‘little impact’
Sleep problems Daytime tiredness	‘several times per week’ ‘every night/day’	‘no’ ‘once or twice’
Headache and/or belly pain	‘headache’ ‘belly pain’ ‘headache’ and ‘belly pain’	no ‘headache’ no ‘belly pain’