ARISe at UMass Chan

Participants' perception of the credibility of the message source will be assessed using a 7-point Likert scale measured across four items. Participants will be asked to rate the following four items on this scale: To what extent do you believe the source of the message to be… (1=not at all, 7=very much so)

• Fair
• Accurate
• Telling the whole story
• Trustworthy

Unit of measure: Scale score 1-7, mean

Perceived message effectiveness will be measured using six items (worth remembering, grabs attention, powerful, informative, meaningful, convincing), each rated on a 7-point Likert scale. The outcome will be the mean of these six ratings for each participant, then averaged by experimental condition.

To what extent is… (1=not at all, 7=very much so)

• The message worth remembering
• The message grabs attention
• This message powerful
• This message informative
• This message meaningful
• This message convincing Unit of Measure: Scale score (1-7, mean across items)

Visual attention, quantified as mean dwell time in milliseconds, will be measured using remote eye-tracking while participants view vaccine promotion messages. Dwell time will be calculated for pre-specified Areas of Interest (AOIs) during the message viewing period. Higher dwell times indicate greater visual attention to the AOIs.

Unit of measure: mean dwell time in milliseconds per message

Reactance will be assessed using four items (irritated, angry, annoyed, aggravated), rated 0 ("None of this feeling") to 4 ("A great deal of this feeling"). The mean reactance score will be calculated for each participant.

How much did this message make you feel the following way? Response options: 0 (None of this feeling) to 4 (A great deal of this feeling).

• Irritated
• Angry
• Annoyed
• Aggravated

Unit of Measure: Scale score (0-4, mean across items)

Description: Assessed with 6 items regarding interpersonal and online sharing, rated 1 (Strongly disagree) to 5 (Strongly agree). The mean score across items will be reported per participant and per condition.

Rate with the following statements on a scale from 1 (Strongly disagree) to 5 (Strongly agree).

Interpersonal setting

• I would be willing to share this information with others.
• I would talk with others about this message.
• I would point others in a direction where they could read this message.

Online setting

• I would be willing to post a link to this information on my social media.
• I would like a social media post with this information.
• I would share a social media post with this information.

Unit of Measure: Scale score (1-5, mean across items)

Vaccine perceptions will be measured using an 8-item scale, administered pre- and post-message exposure. Items are rated from 1 (Strongly disagree/very negative) to 7 (Strongly agree/very positive). Higher scores indicate more positive vaccine perceptions. The outcome will be the mean change in score from pre- to post-exposure.

Unit of Measure: Scale score (1-7, mean change)