Table 3.

Instruments intended to use in the population survey

	Construct	Indicator/instrument
(1)	Health literacy	Labelling (recognition of disease); perceived causes; treatability; effectiveness of treatment options
	Illness perception	Illness Perception Questionnaire (brief version)51
	Illness belief	Eg, ‘Do you think that the person in the vignette has a real disorder?’
(2)	Public stigma	Emotional reactions towards those affected by IBS or fatigue Stereotypes ascribed to persons with IBS or fatigue
	Anticipated stigma	Modified version of the IBS Stigma Scale52
(3)	Illness behaviour	Eg, ‘If you have the feeling of being affected by such complaints, you should get help as soon as possible.’ Healthcare usage
	Illness experience	Own affliction; contact to someone affected
	Treatment experience	Treatment experience
	Somatic symptom burden	Somatic Symptom Scale-853
	Health anxiety	Whiteley Index-754
(4)	Socio-demographic data	Age, sex, educational attainment, occupational position, income, migration status, marital status

IBS, irritable bowel syndrome.