When Celebrities Speak: A Nationwide Twitter Experiment Promoting Vaccination In Indonesia

We ask whether celebrities can help spread information about public health, above and beyond the fact that their statements are seen by many, and ask how they can be most effective in doing so. We conducted a nationwide Twitter experiment with 46 high-profile Indonesian celebrities and organizations, with over 11 million followers, who agreed to randomly tweet or retweet content promoting immunization. Our design exploits the structure of what information is passed on along a retweet chain on Twitter to decompose how celebrities matter. We find that messages that can be identified as being authored by celebrities are 72 percent more likely to be passed or liked compared to similar messages without a celebrity imprimatur. Decomposing this effect, we find that 79 percent of the celebrity effect comes from the act of celebrity authorship itself, as opposed to merely passing on a message. Explicitly citing an external source decreases the likelihood of passing the message by 27 percent. The results suggest that celebrities have an outsize influence in shaping public opinion, particularly when they speak in their own voice.