All items were assessed on a 5-point scale, unless noted otherwise. Composite scores were computed for constructs with multiple items by taking the average of the items. Higher scores indicate higher levels of the construct. Independent samples t-tests were used to compare means by condition.

^aAssessed with two questions (e.g., “HPV can cause anal cancer.”) interspersed among other true/false questions assessing HIV/STI knowledge. Participants received 1 point for each correct response and 0 points for incorrect and “do not know” responses. Points were summed to create a composite score that ranged from 0 to 2.

^bAssessed with one item: “My attitude toward getting vaccinated for HPV in the next 9 months is...” 1 = very negative to 5 = very positive.

^cAssessed with one item: “People who are important to me would want me to get vaccinated for HPV in the next 9 months.” 1 = strongly disagree to 5 = strongly agree.

^dAssessed with four items (e.g., “If you do not get the HPV vaccine, what do you think are the chances that you will get HPV?” 1 = very unlikely to 5 = very likely).

^eAssessed with four items (e.g., “How serious would each of the following be for you: If you developed warts on your penis or scrotum?” 1 = not at all serious to 5 = very serious).

^fAssessed with two items (e.g., “How much regret would you feel if you decided not to get the HPV vaccine and later developed genital or anal warts?” 1 = none to 5 = quite a lot).

^gAssessed with one item: “To what extent is whether or not you get vaccinated for HPV in the next 9 months under your control?” 1 = not at all to 5 = completely.

^hAssessed with one item: “Assuming you wanted to, how hard or easy would it be for you to get vaccinated for HPV in the next 9 months?” 1 = very hard to 5 = very easy.

ⁱAssessed with one item: “I intend to get vaccinated for HPV in the next 9 months.” 1 = strongly disagree to 5 = strongly agree.