Screenshot of PSA at 3 s.
FOX, DISEASE
We tested the PSA’s efficacy through a large randomized controlled trial (RCT) on YouTube, randomizing at the county level and targeting areas that lagged in vaccine uptake. Overall, we spent just under U.S. $100,000 in ads, with a total of 11.6 million ads reaching 6 million unique viewers. These ads appeared before YouTube viewers on mobile phones, TVs, tablets, and computers. Google’s algorithms attached our ad to specific YouTube channels and YouTube posts. The YouTube channel on which Google placed our ad the most was the Fox News channel (playing our ad over 200,000 times on this channel), with the ad displayed before segments of Sean Hannity, Laura Ingraham, Tucker Carlson, and other conservative cable news personalities. As such, our ad likely reached a disproportionately Republican audience, supporting our aim to offer a counter-stereotypical message.We measure the effect of the campaign on county-level vaccination counts in Centers for Disease Control and Prevention (CDC) data. Previous work demonstrates that effects of ads on actual behavior tend to be miniscule and difficult to detect (Our intent-to-treat (ITT) analysis implies that the treatment led to an increase of 103 vaccinations in the average treated county, albeit with a fair amount of uncertainty (with a one-tailed We also take advantage of the detailed engagement data provided by Google Ads tools. These data allow us to observe several alternative measures of treatment intensity in each county, such as how much it cost us (as bidding advertisers) to win the ad auctions corresponding to viewers in each county. Google’s tools also show, for each county, the percentage of viewers who watched at least 10 s of the ad, watched the full ad, or clicked on the ad’s link. In the average county, 41% of YouTube viewers to whom the ad was shown watched at least 10 s of the ad, although they were allowed to skip after 5 s, and 12% watched the full ad. We find that a one-standard-deviation increase in the percentage of viewers watching at least 10 s of the ad increases the number of vaccines distributed in the county by 8.2. A one-standard-deviation increase in the percentage of viewers watching the full ad leads to 12 additional vaccines.We further expand our analysis by examining heterogeneous treatment effects. Among the Trump-leaning counties that comprise our sample, counties that are less heavily Trump-leaning were more responsive to the ad. Specifically, counties below the median level of Trump support (69.4%) saw treatment effects that were larger than counties with greater Trump support, and this difference is large enough and measured with sufficient precision that, in a two-tailed test, it is significant at the 0.10 level when vaccinations are measured in levels and at the 0.05 level when vaccinations are measured in rates.With 1014 treated counties in all, our estimated treatment effect indicates that the total increase in vaccinations from the campaign was 104,036, resulting in about 1 vaccine per dollar in ad spending. Again, we emphasize that the treatment effect is less precisely estimated than would be ideal, but the results taken as a whole suggest that our approach likely made a difference. Combining these estimates with those of Barro (We join a growing body of literature on interventions to increase COVID-19 vaccinations, but our study is distinct in highlighting a political mechanism, and its success for what appears to be a fraction of the cost of other interventions. For example, Thirumurthy 