You don't need a mathematical formula to prove that partisan passions run deep in Congress. But a new study finds that mathematics can ferret out less obvious connections between congressional committees and uncover party-line leanings without any assumptions about the underlying politics at work.
Congress is composed of a network of committees and subcommittees that draft legislation and move it to the full House of Representatives and the Senate for votes. The membership overlap between committees may have a profound impact on political outcomes, much as connections between boards of directors of corporations can influence business deals.
Starting with lists of House committee members in the 102nd through the 107th Congress (1989-2004), applied mathematician Mason Porter of the Georgia Institute of Technology in Atlanta and colleagues used a technique called network analysis to map the arrangement and strength of the connections between committees based on their overlapping members. Previously used to study everything from electrical power grids to the nervous system of worms, the technique revealed that the assignment of members to committees is far from random. This finding was no surprise, but the method also pulled out more subtle patterns in committee membership. For example, the House Committee on Rules has strong connections to both the Select Committee on Homeland Security and the Committee on House Administration. Other committees, such as Energy and Commerce and Ways and Means, are self-contained units.
Porter's team, which reports its findings online this week in Proceedings of the National Academy of Sciences, also related the network connections between committees to the political positions of their members. To avoid making any prior political assumptions, the group used a different mathematical method called single value decomposition to analyze the roll call votes of each member during a session of Congress. The method pinpoints groups that voted similarly on many votes and assigns each member two numbers that enabled the researchers to rank them from least to most partisan. Combining the partisanship measures with the network map, the team found that not only is the Select Committee on Homeland Security one of the committees most tightly linked to another committee (House Rules), but it is also among the most partisan.
The study provides an objective way to answer often-charged political questions about how Congress functions without knowing anything about politics, says applied mathematician Steven Strogatz of Cornell University in Ithaca, New York, who did not take part in the work. "Similar to the method that Google uses to search the Internet, this approach lets the links do the talking."