Social influence and conformity have been thoroughly studied by social psychologists, leading political scientist to the postulation of the bandwagon effect. However, despite its relevance, the bandwagon effect, claiming that seeing pre-election polls makes votes for majority options more likely, has not been properly tested for political voting and evidence regarding this effect is mixed. Experiments either were ran in very abstract contexts only vaguely representing political voting, or only testing the effect of polls on opinions or hypothetical votes . We present an unique experimental design with more realism than previous designs, keeping the experimental control needed to make causal claims.

We tested in an online experiment with 1115 participants from the US how votes change when pre-election polls are shown. Our experimental design is unique in that the votes of the participants have real-world consequences within their electoral area (the US), empower actual political organizations falling on a left-right spectrum, and the votes are on issues currently debated in US politics (firearms, abortion, immigration, and environment). Per issue participants chose between three different charities, representing different positions within the political spectrum. As a result of the experiment 1200$ were distributed across these charities as suggested by the vote.

In line with the bandwagon-effect, we find clear evidence that seeing poll results makes votes for majority opinion more likely. After seeing the surveys, majority opinions received an extra ~7% of votes. In our experiment this effect did not depend on the electoral system and was robust against controlling for the gender and age of voters and the self-assessment on a left-right spectrum. However, we find evidence that under extreme-polarization (where moderate position are the least popular option) the bandwagon-effect is much weaker.