Do voters on the left show more solidarity behaviour? Novel behavioural evidence from interactive surveys in Austria, West and East Germany

Voters on the left typically demand more public redistribution than those on the right. While existing research has demonstrated differences in social behaviour by political ideology, we know little on whether left voters are willing to show more costly solidarity towards others. In this study, we test pre-registered hypotheses on whether the MARPOR left-right score of voters’ preferred party and left-right self-placement predict more solidarity behaviour. We introduce a novel Extended Solidarity Game to measure costly solidarity behaviour as contributions to compensate for income losses of others in randomly assigned groups. The behavioural instrument allows for simultaneous group interactions and was embedded in online surveys in the party system contexts of Austria, West and East Germany. We find evidence for the predicted ideological differences in solidarity: while the MARPOR left-right score shows only a non-significant effect in the expected direction, left-right self-placement (as well as the CHES scores) show a strong, robust and significant effect. The strength of this relationship is highly context-dependent: in Austria and West Germany, predicted contributions of leftmost participants are about 8 percentage points higher than those of rightmost participants. In East Germany, this predicted difference amounts to about 30 percentage points. Additional analyses rule out differences in social trust, economic or cultural political orientations as alternative explanations for the context-dependency of the effect. We argue that the East German party system – characterised by clearer programmatic party differences and more intense party competition – leads voters to define their ideological position more clearly and increases the behavioural relevance of political ideology.