Table 1.

Attributes and levels of the discrete choice experiment.

Attributes	Levels (labels)	Levels (short definition)
Disease	Respiratory disease	The vaccine can protect against a disease with high fever and breathlessness.
	Cancer	The vaccine can protect against a cancer, which could occur 20 years from now.
	Genital warts	The vaccine can protect against genital warts.
Safety	No side effect	The vaccine does not cause serious side effects.
	Scientific surveillance	The vaccine’s safety has been monitored for more than 10 years worldwide. No serious side effect has been scientifically confirmed.
	Safety other countries	In countries where most adolescents are vaccinated, the risk of a serious side effect that could be due to vaccination has not increased.
	Benefit/risk	The vaccine can only on rare occasions cause a serious side effect, but the benefits from vaccination are much greater than its risk.
Indirect Protection	Protects only you	The vaccine protects only you.
	Protects others	By getting vaccinated, you can avoid transmitting the infection to other persons.
	Elimination	By vaccinating most young people of your age, one can make the disease disappear from the population.
Coverage	Not enough	Not enough adolescents of your school have registered to get vaccinated.
	Already one third	Already one-third of adolescents of your school has registered to get vaccinated.
	Most adolescents	Most adolescents of your school have registered to get vaccinated (80%).
	Other countries 80%	In some countries like England and Portugal, more than 80% of adolescents are vaccinated.