Introduction MPs represent citizens in Parliament but face pressure from interest groups.

Problem/Argument This creates a tension between constituent preferences and lobbying influences.

• Do sectional groups incentivize MP defections?
• Is there an alternative path toward authentic representation?

Data & Methods We analyzed 118 Swiss public referenda using multilevel regression to compare voter preferences with MPs' voting behavior across 448 representatives.

Key Findings Our results highlight two divergent effects:

• Negative effect: Sectional groups correlate strongly with MP defections from constituent views (bullet point).
• Positive effect: Cause groups reinforce the connection between MPs and voters, improving representation quality.

Significance These findings offer a nuanced understanding of political influence in Switzerland — interest group strategies matter differently depending on their type.