When Celebrities Speak: A Nationwide Twitter Experiment Promoting Vaccination in Indonesia. 2018.Abstract.
Celebrity endorsements are often sought to influence public opinion. We ask whether celebrity statements actually lead people to change their beliefs, and whether their endorsement per se has an effect beyond the fact that their statements are seen by many. To unpack these effects, we conducted a nationwide Twitter experiment in Indonesia with 46 high-profile celebrities and organizations, with a total of 7.8 million followers, who agreed to let us randomly tweet or retweet content promoting immunization from their accounts. By randomizing which celebrities tweeted when, we show that exposure to the campaign can influence beliefs about vaccination, and appears to increase knowledge of immunizationseeking behavior by one's neighbors and friends. Our design then exploits the structure of what information is passed on along a retweet chain on Twitter to parse reach versus endorsement effects. We find consistent evidence that endorsements matter per se: tweets that users can identify as being originated by a celebrity are far more likely to be liked or retweeted by users than similar tweets seen by the same users but without the celebrities' imprimatur. By contrast, citing sources explicitly actually reduces diffusion. Taken together, the findings suggest an important role for celebrity endorsement.