Responses to E-cigarette Message Source and Presentation

Participants' self-reported message acceptance were measured by using a five-point Likert scale using five items assessing whether participants thought the message was worth remembering, grabbed their attention, powerful, convincing, and meaningful on a scale from 1 (Strongly disagree) to 5 (Strongly agree). Items were summed and averaged to create a single composite score, and this was done for each arm for each vaping status. Higher scores indicate more more message acceptance, therefore better outcomes.

Harm perceptions was measured by a single item e-cigarette harm perceptions question assessing participants' perceived absolute harm of e-cigarette use on a scale from 1 (Not at all harmful) to 10 (Very harmful). Items were summed and averaged to create a single composite score. This was done for each vaping status (current vapers and susceptible non-vapers). Higher scores indicate greater vaping harm perceptions, therefore indicating better outcome.

Negative cognition was measured by six-item reactance questionnaire, such as perceptions of messages being manipulative, misleading, distorted, overblown, exaggerated, and overstated on a scale from 1 (Strongly disagree) to 5 (Strongly agree). Higher scores indicate greater negative cognition, indicating worse outcome.

Message anger was measured by four item message anger question assessing the extent to which the messages made participants feel irritated, angry, annoyed, and aggravated on a scale from 1 (not at all) to 5 (very much). Items were summed and averaged. This was done for each vaping status (current vapers and susceptible non-vapers). Higher scores indicate greater anger toward messages, indicating worse outcomes.

Message liking will be measured by a single-item liking of the message on scale from 1 (Dislike very much) to 5 (Like very much). Items were summed and averaged to create a single composite score. This was done for each vaping status (current vapers and susceptible non-vapers). Higher scores indicate greater message liking, therefore indicating better outcome.

Source trust was measured by a single-item trust in health information source questionnaire, such as trust in source about vaping information on a scale from 1(Not at all) to 5 (Very much so). Items were summed and averaged to create a single composite score. This was done for each vaping status (current vapers and susceptible non-vapers). Higher scores indicate greater source trust, therefore indicating better outcome

Participants' self-reported vaping attitudes were measured by using a five-point bipolar scale using 7 subscale items assessing whether participants thought vaping was enjoyable, healthy, safe, fun, smart, cool, and attractive on a scale from 1 (negative attitudes) to 5 (positive attitudes). Items were summed and averaged to create a single composite score, and this was done for each arm for each vaping status. Higher scores indicate more positive e-cigarette attitudes, therefore worse outcomes.

Participants' vaping or vaping trial intentions were measured by using a 3 subscale items assessing participants' intentions to vape: soon/anytime during the next year/would use offered by one of their best friends, on a scale from 1 (Definitely not) to 5 (Definitely yes). Items were summed and averaged to create a single composite score. This was done for each vaping status (current vapers and susceptible non-vapers). Higher scores indicate greater vaping intentions, therefore indicating worse outcome.