The order effects of humor and risk messaging strategies in public service advertisements: the moderating role of trust in science and mediating role of psychological reactance

Humor and risk elements are often used together in public service advertisements (PSAs), but limited research has been conducted on how the order in which they are presented contributes to PSA effectiveness. To address this question, this study examined the impact of two health messaging strategies (humor and risk) and their order effects in PSAs promoting COVID-19 and flu vaccination on persuasion outcomes, with psychological reactance and perceived PSA effectiveness as serial mediators, and trust in science as a moderator. The findings from the COVID-19 vaccination context showed that a humor-then-risk (risk-then-humor) structure predicted a decrease in reactance for participants with lower (higher) trust in science. For low-trust participants, a humor-then-risk order resulted in greater intentions to vaccinate through reduced reactance and increased perceived PSA effectiveness. In the flu vaccination context, only among individuals with high trust in science, the order effect—risk-then-humor—was effective in reducing reactance and promoting vaccination intention through increased perceived PSA effectiveness.