Community Structure in Congressional Cosponsorship Networks (original) (raw)
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Party polarization in congress: A social networks approach
arXiv preprint arXiv: …, 2009
We use the network science concept of modularity to measure polarization in the United States Congress. As a measure of the relationship between intra-community and extra-community ties, modularity provides a conceptually-clear measure of polarization that directly reveals both the number of relevant groups and the strength of their divisions. Moreover, unlike measures based on spatial models, modularity does not require predefined assumptions about the number of coalitions or parties, the shape of legislator utilities, or the structure of the party system. Importantly, modularity can be used to measure polarization across all Congresses, including those without a clear party divide, thereby permitting the investigation of partisan polarization across a broader range of historical contexts. Using this novel measure of polarization, we show that party influence on Congressional communities varies widely over time, especially in the Senate. We compare modularity to extant polarization measures, noting that existing methods underestimate polarization in periods in which party structures are weak, leading to artificial exaggerations of the extremeness of the recent rise in polarization. We show that modularity is a significant predictor of future majority party changes in the House and Senate and that turnover is more prevalent at medium levels of modularity. We utilize two individual-level variables, which we call "divisiveness" and "solidarity", from modularity and show that they are significant predictors of reelection success for individual House members, helping to explain why partially-polarized Congresses are less stable. Our results suggest that modularity can serve as an early-warning signal of changing group dynamics, which are reflected only later by changes in formal party labels.
Connecting the Congress: A Study of Cosponsorship Networks
Using large-scale network analysis I map the cosponsorship networks of all 280,000 pieces of legislation proposed in the U.S. House and Senate from 1973 to 2004. In these networks, a directional link can be drawn from each cosponsor of a piece of legislation to its sponsor. I use a number of statistics to describe these networks such as the quantity of legislation sponsored and cosponsored by each legislator, the number of legislators cosponsoring each piece of legislation, the total number of legislators who have cosponsored bills written by a given legislator, and network measures of closeness, betweenness, and eigenvector centrality. I then introduce a new measure I call "connectedness" which uses information about the frequency of cosponsorship and the number of cosponsors on each bill to make inferences about the social distance between legislators. Connectedness predicts which members will pass more amendments on the floor, a measure that is commonly used as a proxy for legislative influence. It also predicts roll call vote choice even after controlling for ideology and partisanship.
Legislative Cosponsorship Networks in the U.S. House and Senate
In the US House and Senate, each piece of legislation is sponsored by a unique legislator. In addition, legislators can publicly express support for a piece of legislation by cosponsoring it. The network of sponsors and cosponsors provides information about the underlying social networks among legislators. I use a number of statistics to describe the cosponsorship network in order to show that it behaves much differently than other large social networks that have been recently studied. In particular, the cosponsorship network is much denser than other networks and aggregate features of the network appear to be influenced by institutional arrangements and strategic incentives. I also demonstrate that a weighted closeness centrality measure that I call "connectedness" can be used to identify influential legislators.
Party polarization in congress: A network science approach
2009
We measure polarization in the United States Congress using the network science concept of modularity. Modularity provides a conceptually-clear measure of polarization that reveals both the number of relevant groups and the strength of inter-group divisions without making restrictive assumptions about the structure of the party system or the shape of legislator utilities. We show that party influence on Congressional blocs varies widely throughout history, and that existing measures underestimate polarization in periods with weak party structures. We demonstrate that modularity is a significant predictor of changes in majority party and that turnover is more prevalent at medium levels of modularity. We show that two variables related to modularity, called 'divisiveness' and 'solidarity,' are significant predictors of reelection success for individual House members. Our results suggest that modularity can serve as an early warning of changing group dynamics, which are reflected only later by changes in party labels.
The Rise of Partisanship and Super-Cooperators in the U.S. House of Representatives
PLOS ONE, 2015
It is widely reported that partisanship in the United States Congress is at an historic high. Given that individuals are persuaded to follow party lines while having the opportunity and incentives to collaborate with members of the opposite party, our goal is to measure the extent to which legislators tend to form ideological relationships with members of the opposite party. We quantify the level of cooperation, or lack thereof, between Democrat and Republican Party members in the U.S. House of Representatives from 1949-2012. We define a network of over 5 million pairs of representatives, and compare the mutual agreement rates on legislative decisions between two distinct types of pairs: those from the same party and those formed of members from different parties. We find that despite short-term fluctuations, partisanship or non-cooperation in the U.S. Congress has been increasing exponentially for over 60 years with no sign of abating or reversing. Yet, a group of representatives continue to cooperate across party lines despite growing partisanship.
Journal of Complex Networks, 2016
We study community structure in time-dependent legislation cosponsorship networks in the Peruvian Congress, and we compare them briefly to legislation cosponsorship networks in the US Senate. To study these legislatures, we employ a multilayer representation of temporal networks in which legislators in each layer are connected to each other with a weight that is based on how many bills they cosponsor. We then use multilayer modularity maximization to detect communities in these networks. From our computations, we are able to capture power shifts in the Peruvian Congress during 2006-2011. For example, we observe the emergence of 'opportunists', who switch from one community to another, as well as cohesive legislative communities whose initial component legislators never change communities. Interestingly, many of the opportunists belong to the group that won the majority in Congress.
2011
Abstract This project examines how interest groups create partisan connections among US House members. Although the rise of ideologically motivated groups has been identified as a potential cause of legislative partisanship, there is very little research on how interest groups affect the nature of partisan coalitions. We consider how interest group donation strategies create connections between legislators and how the resulting networks affect the nature of lawmaking in the House.
Networks in the Legislative Arena: How Group Dynamics Affect Cosponsorship
Legislative Studies Quarterly, 2011
In this study, we explore the determinants of cosponsorship activity within state legislatures. Previous literature has generally focused on individual level characteristics to explain legislative behavior, placing little emphasis on how collaboration and mutual interests shape the agenda-setting process. Utilizing a social dynamics framework, we develop and test a model of the interplay of the activities of sponsorship and cosponsorship that includes both individual-level and social network characteristics as determinants of agenda-setting behavior. We find several consistent factors that influence the frequency of activity: 1) ideological distance (the further the distance between the primary sponsor and a legislator, the less likely that legislator will cosponsor a measure) 2) the proximity of legislators' districts (legislators are more likely to cosponsor measures that are sponsored by legislators from neighboring districts) 3) homophily (legislators who share similar characteristics such as race, gender, and ethnicity are more likely to cosponsor each other's measures) and 4) transitivity (legislators who cosponsor the legislation sponsored by their colleagues are more likely to attract those colleagues as cosponsors on their own set of sponsored measures). Further, our analysis of network structure suggests that legislators in each state are organized into relatively small groups, exhibiting a "clique-like" quality, whereby members coalesce around several common traits and cosponsor each other's measures.
Multiplex Legislative Networks and the Power of Caucuses to Alleviate Partisan Polarization
2013
Congress has been increasingly criticized as a broken, gridlocked, polarized, ineffective institution. In this paper we seek to explore the consequences of polarization and whether legislators take steps to alleviate them. We hypothesize that participation in the voluntary, bipartisan, caucus system provides opportunities for legislators to build cross-partisan relationships and prot from shared information, which can alleviate some of the negative eects of polarization. We operationalize polarization using dyadic covoting and show that legislators are more likely to covote if they share more caucus connections, controlling for a variety of factors that predict voting. The data in this analysis spans 9 congresses (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) and includes multiple connections between legislators. *
The Agreement Score: Legislative Networks and Ideology
A number of scholars have described a steady increase in ideological polarization between Democrats and Republicans in the U.S. Congress. This research often relies upon ideal point estimation methods that assume legislators are atomistic individuals registering a sincere, independent preference on each roll call vote. Yet scholars who employ social network techniques, such as estimating each legislator's centrality score, typically assume that legislators' voting decisions are a consequence of social influences. This paper examines the distinctions between these two approaches. We introduce the agreement score, which measures the extent to which pairs of legislators vote the same way. We demonstrate the relationship between both agreement scores and centrality scores, a common measurement of influence in social network analysis, as well as between centrality scores and ideal point estimates. We then focus the ways in which agreement scores can be used to illuminate theories of legislative polarization for members of the U.S. House from 1967 to 2008. Agreement scores are not only more conducive to the assumptions typically made in social network analysis but also the empirical patterns of these scores are consistent with major explanations of legislative partisanship.