Access to information about candidates' performance has long stood as a key factor shaping voter behaviour but establishing how it impacts behaviour in real-world settings has remained challenging. In the 2018 Brazilian presidential elections, unpredictable technical glitches caused by the implementation of biometrics as a form of ID led some voters to cast ballots after official tallies started being announced. In addition to providing a source of exogenous variation of information exposure, runoff elections also enable us to distinguish between different mechanisms underlying the impact of information exposure. We find strong support for a vote-switching bandwagon effect: information exposure motivates voters to abandon losing candidates and switch support for the frontrunner---a finding that stands in the second round when only two candidates compete against each other. These findings provide theoretical nuance and stronger empirical support for the mechanisms underpinning the impact of information exposure on voter behaviour.
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