Plurality rules constraint party competition and create two-party elections. There is abundant empirical evidence in the literature validating this reduction effect. However, empirical studies based on observational data can hardly disentangle the share of reduction that is attributable to candidates that decide no to enter elections for which they are not viable, and to voters that vote strategically to maximize their impact on the electoral outcome. To fill this gap, we conducted a laboratory experiment replicating real-life elections under plurality rules where subjects play, alternatively, the role of voters and candidates. We find that the share of reduction of candidates is slightly more important than the one of voters. We conclude that candidates play a key role in the effect of electoral rules on party competition.
