When Messaging Norms Meet Platform Norms: Two Experiments on Short-Video Persuasion and Misinformation Correction

Short-form video platforms such as TikTok are transforming health communication while amplifying the risks of misinformation. This study employs a sequential two-experiment design to examine (1) how norms in messaging (narrative vs. non-narrative descriptive norms) interact with norms on the platform (social endorsement: high vs. low) to shape message credibility, and (2) how misinformation endorsement (high vs. low) interacts with platform intervention labels (present vs. absent) to influence attitudes and intentions toward human papillomavirus (HPV) vaccination. Study I (N = 255) shows that high social endorsement enhances credibility, whereas narrative framing provides no additional persuasive benefit, suggesting that algorithmic popularity cues overshadow narrative effects. Study II (N = 299) reveals that highly endorsed misinformation undermines affective attitude when labels are absent, but subtle warnings reverse this effect. Affective attitude primarily drives behavioral intention under misinformation exposure. The findings extend norm-based persuasion and misinformation correction theories within algorithmic short-form video environments.