Indeed, your article was by far the easiest to code 🙂. That really reflects the clarity and transparency of your reporting—much appreciated!

Thank you for all the help and guidance! I couldn't ask for a better mentor 🫶

No, Qinyu, you rock 🥹

The article is open access 🔓, preregistered 📑, and fully transparent: we share all data, effect size computations, screenshots of extracted effects, and full analysis code. 🧑‍💻📂 Just see the post above.

That's all! End of thread! Thanks for your attention <3

📖 doi.org/10.1080/1743...

📂 osf.io/zm9at/

📝 Preregistration: PROSPERO CRD42024540536

Personal note: this is the most work I’ve ever put into a project (yet). I learned so much, and I’m grateful to see it published. With vaccine hesitancy rising, it’s important to remember that every (non-)vaccination also has a social impact

Takeaway 💡
Communicating herd immunity has a small but positive effect on vaccination motivation. However, the effect is larger when people can experience it (VR, simulations) instead of just reading text. 🚀

As such, future messages must be clear, engaging & immersive 🕶️💉

We also ran some fancy machine learning 🧠, multiple tests for publication bias (spoiler: none found ✅), assessed Risk of Bias (all good), and packed in plenty of other cool stuff (including a HUGE table 📊).
For all the details—you’ll have to check out the paper 😉

Among the most relevant moderators, we identify the medium of communication. When people can actually experience herd immunity (e.g., VR, simulations), the effect on vaccination motivation more than doubles (g = 0.29) 🚀

📊 Herd immunity messages do boost vaccination motivation! We find a small but positive summary effect: g = 0.12 (95% CI: 0.08–0.17) 📈 But averages only tell part of the story—what’s even more interesting is when and how these messages work. That’s what we tested next.

To find out, we ran the first systematic review & meta-analysis on herd immunity communication 🧪
🔎 10+ years of experimental work
📂 a whole lot of records screened
📊 43 studies (67 effects), >100k participants
⚙️ Three-level model + Publication Bias Tests + MetaForest

So… what did we discover? 👀

💉 Communicating HI could have different effects:
👉 It could motivate prosocial vaccination (“I’ll vaccinate to protect others”)
👉 But it could also motivate selfish-rational non-vaccination (“I’m safe if others vaccinate”)

Which is it? Does communicating HI help vaccination motivation? 🤔

Vaccines are a huge achievement ❤️💉. By getting vaccinated, you not only protect yourself but also protect others indirectly, as it is more difficult for the pathogen to spread. This is a simplified explanation of herd immunity (HI).

Yet, communicating HI could lead to several outcomes💉🤔