Beyond Average Effects: How Advice Quality and Congruence Impact on Party Preferences

Voting Advice Applications (VAAs) have become widely used tools for political information provision, yet experimental research has focused almost exclusively on average treatment effects. This conceals critical variation in when and for whom VAAs influence party preferences. Drawing on data from randomized experiments across five countries, we move beyond aggregate effects to examine the sources of heterogeneous treatment effects. We show that VAA advice does not affect all voters equally: effects are shaped by advice characteristics and their alignment with prior preferences. High-quality advice produces stronger effects than ambiguous recommendations. Crucially, advice congruence matters: voters respond differently when VAA recommendations confirm rather than challenge their existing preferences. These moderating factors interact, revealing that advice quality matters most when recommendations are incongruent. By identifying conditions under which VAAs shape preferences, we advance understanding of political information processing. Our findings have practical implications for VAA design and theoretical implications for how voters process algorithmic political advice.