Table 2.

Questionnaire with social cognitive determinants

Determinant	Number of items	r or Cronbach's alpha	Example question	All questions were rated ‘completely agree – completely disagree’, except for:
Intention	2	.81	I will do a chlamydia test in the coming three months;	Question was rated ’not very probable - very probable’
Attitude	5	.73	When I take a chlamydia test, for me that would be..	Questions were rated ’very unpleasant - very pleasant’, very annoying - very enjoyable’, an extreme bad idea - an extreme good idea’, very unimportant - very important’, and ’very threatening - very safe’.
Susceptibility	4	.68	It is possible that I’ve had sex with someone with chlamydia
Severity (1–8)	1	-	Eight different health issues had to be ranked from 1 to 8 based on how severe it would be to get the health issue within 12 months. The eight health issues were ’hearing impairment’, “Pfeiffer disease”, “chlamydia”, “Repetitive Strain Injury (RSI)”, “Lyme disease”, “Caries”, “Heart attack”, and “HIV/AIDS”.
Unrealistic optimism	2	.65	The chance that I will get chlamydia compared to someone of the same gender and age is…	Question was rated ’much larger - much smaller’
Subjective norm	3	.82	My family thinks that I should get a chlamydia test in the coming three months
Descriptive norm	3	.88	My friends takes a chlamydia test
Moral norm	2	.70	It would be wrong if I don’t take a chlamydia test
Perceived behavioral control	3	.87	If I want to, I’m sure that I can do a chlamydia test in the coming three month.
Outcome expectations	2	.77	If I would take a chlamydia test, it would give certainty about my health	Question was rated ‘very unlikely - very likely’
Barriers	3	-	Three potential barriers (mentioned in earlier studies [5,6] for non participation were questioned: the barrier of having no time, no internet access, or the barrier of not willing to test (‘don’t feel like testing’).