Table 1.

Study arms.

	Study arm 1 n=249	Study arm 2 n=251	Study arm 3 n=250
Initial invitation	Web-based questionnaire	Web-based questionnaire	Web- and paper-based questionnaire
First reminder (after 3 weeks, in case of no response to initial contact)	Web-based questionnaire	Web- and paper-based questionnaire	Web based and option to apply for new paper-based questionnaire
Second reminder (after 3 weeks, in case of no response to 1st reminder)	Web- and paper-based questionnaire	Web-based and option to apply for new paper-based questionnaire	Telephone contact
Third reminder	Telephone contact	Telephone contact