Table 1.

Overview of primary and secondary outcome measures.

Measures and items					Score/scale (minimum to maximum value)	Cronbach alpha (α) or Pearson r (r)2	References
Primary outcome
	HPV a vaccination uptake				0=not vaccinated, 1=vaccinated	N/Ab
		Uptake of the HPV vaccination is obtained through data from Praeventis.
Secondary outcomes
	IDM c outcome (dichotomous)				0=not informed, 1=informed	N/A	[16], [34], [36]
		An informed decision has been made when:
			The knowledge score was higher or equal to the mean of knowledge at baseline, the attitude score was higher than 4 (positive) and the HPV vaccination has been received.
			The knowledge score was higher or equal to the mean of knowledge at baseline, the attitude score was lower than 4 (negative), and the HPV vaccination has not been received.
			Any other combination was categorized as an uninformed decision.
	IDM outcome (continuous)				0=least informed decision to 48=most informed decision	N/A	[16], [34], [38]
		Attitude was recoded from 0-7 to −3 (negative) to 3 (positive attitude) and HPV uptake was recoded from 0 or 1 to −1 (no injection) or 1 (1 or 2 injections).
		Level of consistency was measured by multiplying the scores for attitude by those for HPV uptake (−3=low consistency; 3=high consistency). Consistency was then recoded into 0 (low) to 6 (high). Both consistency and sufficient knowledge were considered prerequisite for an informed decision.
		Knowledge scores (−8=low; 8=high) lower or equal to 0 were considered insufficient (0=no insufficient knowledge; 8=high knowledge).
		The level of IDM outcome was determined by multiplying the scores for knowledge with those for consistency.
	Decisional conflict about the HPV vaccination				1=high to 7=low decisional conflict	.94 (α)	[17]
		As regards the HPV vaccination:
			I felt sure about my choice
			The decision was relatively easy to make
			I was clear about the best choice for my daughter
	HPV vaccination intention				1=low intention to vaccinate to 7=high intention to vaccinate	.92 (r)	[7,8]
		Are you planning on getting your daughter vaccinated against HPV?
		How big is the chance that you will get your daughter vaccinated?
	Attitude toward the HPV vaccination				1=negative to 7=positive attitude	.98 (α)	[38]
		Vaccinating my daughter against HPV is...
			very undesirable to very desirable
			very bad to very good
			very negative to very positive
			very unimportant to very important
	Risk perception (having received no HPV vaccination)				1=low to 7=high risk perception	N/A	[38,39]
		Imagine that your daughter was not vaccinated against HPV.
			The chance that my daughter will get cervical cancer is...
	Risk perception (having received the HPV vaccination)				1=low to 7=high risk perception	N/A	[38,39]
		Imagine that your daughter was vaccinated against HPV.
			The chance that my daughter will get cervical cancer is...
	Anticipated regret about rejecting the HPV vaccination				1=low to 7=high anticipated regret	N/A	[7,8]
		Imagine your daughter has not received the HPV vaccination and she gets cervical cancer in the future.
			How much would you regret your decision to let her receive no vaccination?
	Beliefs about the HPV vaccination				1=negative to 7=positive beliefs about the HPV vaccination	.85 (α)	[39,40]
		If the government offers the vaccination, I assume it will be safe.
		Our government shows responsibility for the health of the Dutch population by introducing the HPV vaccination.
		The HPV vaccination was only introduced because the pharmaceutical industry will earn a lot of money from it (R).
		There is too little known about whether the HPV vaccination effectively protects against cervical cancer (R).
		There is too little known about the detrimental side effects of the HPV vaccination (R).
		My daughter is too young to receive the HPV vaccination (R).
		My daughter does not need the vaccination because she is not yet sexually active (R).
	Subjective norms toward the HPV vaccination d				−20=negative to 20=positive	.64 (r)	[38]
		Normative beliefs:
			Regarding the HPV vaccination of your daughter, what is your expectation on the opinion of...
				Social referents: partnere, daughter
		Motivation to comply:
			How motivated are you to comply with the opinion of...?
	Habit strength toward the HPV vaccination				1=weak to 7=strong habit strength	.78 (r)	[41]
		Letting my daughter receive the HPV vaccination is something I do:
			automatically
			without thinking
	Self-efficacy expectations toward the HPV vaccination				1=low self-efficacy to 7=high self-efficacy	.82 (α)
		To what extent would you succeed in dealing with the following statements?
			Guiding my daughter in the decision regarding the HPV vaccination
			Having a good talk with my daughter about the HPV vaccination
			Having a good talk with my partnere about the HPV vaccination
			Motivating my daughter to have herself vaccinated
			Getting the actual HPV vaccination/2 injections with my daughter
	Knowledge about the HPV vaccination f				−8=incorrect, 8=correct	N/A	[7,8]
		Are the following statements true or false?
			HPV is sexually transmittable.
			Condoms fully protect against HPV.
			My daughter is obliged to get the HPV vaccination when she is invited.
			You will always notice when you are infected by HPV.
			Only women can get infected by HPV.
			Women who received the HPV vaccination are still advised to participate in the cervical cancer screening in the Netherlands.
			The HPV vaccination fully protects against cervical cancer.
			My daughter does not need to get the HPV vaccination if she is already sexually active.
	Relative effectiveness of the HPV vaccination g				−9=HPV vaccination least effective to 9=HPV vaccination most effective	N/A	[7,8]
		How would you rate the effectiveness of the following methods of preventing cervical cancer:
			having safe sex
			having sex with only 1 person in a lifetime
			participating in the cervical cancer screening
			having a healthy lifestyle (eg, not smoking)
			the HPV vaccination
			Participants rated the effectiveness of each method

^aHPV: human papillomavirus.

^bN/A: not applicable.

^cIDM: informed decision making.

^dThe subjective norms score was first computed by multiplying normative beliefs and motivation to comply for each social referent, and then by summing up the multiplications of the social referents.

^eOnly applicable if the mother indicated that she had a partner.

^fKnowledge is not a scale because the answer on 1 item does not predict the answer on other items; the items were summed up to present a sum score of knowledge.

^gThe difference between the rated effectiveness of the HPV vaccination and the most effective alternative represented the relative effectiveness score (−9=HPV vaccination least effective to 9=HPV vaccination most effective).