When "Others" Seem More Gullible: A Measles Outbreak and the Third-person Effect
A real-world example of Third-person effect in action
Context
A mid-sized city's public health department monitored growing anti-vaccine content on social media during an early-spring measles season. Leadership felt confident that most local parents were rational and well-informed, while assuming the real danger was that people in other neighborhoods or online communities would be swayed.
Situation
Faced with rising misinformation posts, the department produced a single, broadly worded press release and posted general educational graphics to its social channels rather than launching targeted outreach. They prioritized speed and scale of messaging over tailored engagement with vulnerable subcommunities.
The bias in action
Decision-makers exhibited the third-person effect by assuming that the misinformation would affect "other" parents more than their own population — they believed their local community would see through scare tactics. That belief reduced perceived urgency for micro-targeted interventions (e.g., door-to-door outreach, clinics in high-risk neighborhoods, or partnering with local faith and school leaders). They also discounted anecdotal reports from school nurses as isolated rather than symptomatic of wider persuasion. Because they underestimated how persuasive the online content could be for their own residents, resources were allocated to one-size-fits-all messaging instead of rapid, localized countermeasures.
Outcome
Over the next six weeks, vaccination appointment bookings in two adjacent neighborhoods declined noticeably and a cluster of measles cases emerged in schools serving those neighborhoods. The city required emergency vaccination clinics and temporary school exclusions to contain spread, incurring unplanned costs and community disruption.