The effect of social media ads on election outcomes

Social media has become a key communication channel in politics and allows for political advertising with wide reach yet low costs. However, the effect of political ads from social media on election outcomes is largely unclear. Here, we aim to estimate the association between online political advertising and election outcomes during the 2021 German federal election. For this, we analyze a unique, large-scale dataset of 21,641 political ads from Facebook and Instagram that received ~126 million impressions. Using regression analysis, we show that political advertising on social media has a positive relationship with a candidate's election outcome and may even sway elections. All else equal, ~200,000 additional impressions are predicted to increase a candidate's votes by 2.1%. Generally, establishing causality in the context of election outcomes is difficult. Here, we use a state-of-the-art causal sensitivity analysis, which allows us to evaluate how unobserved confounding may affect our estimates. We find that the estimated effects cannot be reasonably explained away, which implies that social media ads have a causal effect on election outcomes. Together, our results highlight the significance of social media for election outcomes.