Outcome measures and statistical an

Outcome measures and statistical analysis
For the analyses reported in this paper, original data at the individual level were aggregated up to the advert level (n=37), meaning that the responses of all youth who viewed and rated a particular advert were averaged for that advert. These responses should be interpreted as the proportion of youth related to a specific outcome. For example, for advert recall, the variable reflects the mean proportion of youth exposed to that advert that subsequently recalled the advert in the follow up interview. Outcome variables for this study included meas- ures of appraisal and engagement. Appraisal included two measures obtained from the rating sessions: (a) how good (“Overall, I thought this ad was a very good anti-smoking advertisement”); and (b) stand out (“Which one of these ads will most make you stop and think?”). Engagement included three measures obtained during the follow up sessions: (a) recall (the proportion of youth from each rating session who recalled each specific advert at follow up); (b) thought about (the proportion of youth from each rating session who reported having thought about the advert between the rating session and follow up; and (c) discussed (the proportion of youth from each rating session who reported having discussed the advert between the rating session and follow up with someone not in the rating session).