Analyzing Co-Sponsorship Networks from 127 Years of the Swiss Federal Assembly

Analyses of legislative behavior is often based on ideological positions (or policy preferences) of the involved actors, such as parties or individual members of parliament (MPs). These positions allow for detailed analysis on how political alliances are formed and leveraged to influence the decision-making process in their favor. Over the years the discipline has generated and adapted different methods and measures to estimate ideological positions of political actors. These measures are based on a variety of data sources, such as roll-call voting behavior in parliament, surveys, social media behavior or campaign contributions of MPs. Most of these measures have constraints, either methodologically or based on data availability. Roll-call votes are only informative if this form of voting is standard in a parliament; surveys only report snapshots of positions and are often not answered by all MPs; social media behavior depends on the availability of profiles; and campaign contributions have to be public record.

We propose to leverage a new longitudinal data set based on the proceedings of the Swiss Federal Assembly from 1891 to 2019 (see our DemocraSci project). Instead of looking at roll-call votes, which are non-standard in Swiss parliamentary history, or relying on surveys or social media appearances, we use speeches and legislative co-sponsorship signatures to elicit political positions of MPs. Since parliamentary alliances in Switzerland are dynamic and depend less on party memberships and more on the policy issue at hand, we present new ideological measures that are both issue-dependent and time-dependent. Issue-dependent ideological measures allow for more detailed and multidimensional political space and have been show to be a significant improvement over conventional measures. Time-dependent ideological positions allow more detailed analyses on how and why MPs change their opinion or adapt their positions. We propose an innovative new measure of time-dependent ideological positions and use them to study how legislative collaborations over time shape these positions.

With our issue- and time-dependent measures of political positions we study how institutional changes affected polarization levels in the Swiss Federal Assembly, how party fusions and splits are the product of shifting ideological positions and whether legislative collaborations arise due to shared ideological positions or are shaped by previous collaborations and interactions. Thus, our analyses as well as our data sets and methods will uncover new insights into (Swiss) parliamentary research.