Cosponsorship Data 280,000 bills proposed in the U.S. House and Senate from 1973 to 2004 (93rd-108th Congresses) recorded in Thomas over 2.1 million cosponsorship.

Cosponsorship Data

280,000 “bills” proposed in the U.S. House and Senate from 1973 to 2004 (93rd-108th Congresses) recorded in Thomas

over 2.1 million cosponsorship signatures partitioned by chamber and Congress to create

32 separate cosponsorship networks http://jhfowler.ucsd.edu/cosponsorship.htm

Cosponsorship in the House

Cosponsorship in the Senate

Mutual Cosponsorship Relations

Connectedness: An Alternative Measure

Traditional measures of centrality generate plausible names None takes advantage of information about the strength of social

relationships Total number of cosponsors on each bill

Legislators recruit first those legislators to whom they are most closely connected. More cosponsors = lower probability of direct connection Bills with fewer total cosponsors more reliable Strength of the connection between i and j = 1/cij

Total number of bills sponsored by j and cosponsored by i More bills in common = stronger relationship

Weighted cosponsorship distance

Weighted cosponsorship distance

Legislative connectedness

Suppose direct distance from legislator j to legislator i is simple inverse of the cosponsorship weight

Then use Dijkstra’s algorithm (Cormen et al. 2001) Starting with legislator j, identify from a list of all other legislators the

closest legislator i Replace each of the distances with Remove legislator i from the list and repeat until there are no more

legislators on the list. Connectedness is the inverse of the average of these distances from all other legislators to legislator j.

Results for the House

Results for the Senate

Quality of Strongest Weighted Relationships

Institutional Ties House committee chairs and ranking members Senate majority and minority leaders

Regional Ties From the same state In the House they are often from contiguous districts

Issue Ties Rep. Jim DeMint and Sue Myrick -- Republican Study Committee Sen. George Mitchell and Jim Sasser -- Federal Housing Reform Sen. Kay Bailey Hutchinson and Sam Brownback -- marriage penalty relief and

bankruptcy reform Personal Ties

Senator John McCain chaired Senator Phil Gramm’s 1996 Presidential campaign McCain has told the media that they have been friends since 1982 when they

served together in the House (McGrory 1995)

108th House Top 20

108th Senate Top 20

External Validity: Legislative Influence

Widely used measure of legislative influence is number of successful floor amendments Hall 1992; Sinclair 1989; Smith 1989; Weingast

1991 1 SD increase in connectedness increases

successful floor amendments 53% in House 65% in Senate

External Validity: Roll Call Votes

Model roll call votes as in Poole and Rosenthal, adding connectedness score of sponsor

1 SD increase in connectedness of sponsor increases votes for bill by 5.2 in House 8.2 in Senate

2 SD increase would change 16% of House votes and 20% of Senate votes

Landmark Legislation:An Alternative to Mayhew

Modularity(Newman and Girvan 2004)Define modularity to be

Q = (number of edges within groups) – (expected number within groups).

Actual Number of Edges between i and j is

Expected Number of Edges between i and j is

Modularity Matrix So Q is a sum of

over pairs (i, j) that are in the same group Or we can write in matrix form as

Where B is a new characteristic matrix, the modularity marix,

(si, sj)

Modularity Matrix

Algorithm Calculate the leading eigenvector of the

modularity matrix Divide the vertices according to the signs of the

elements

Note that there is no need to forbid the solution with all the vertices in a single group.

Example

Example Applications

Books on politics The vertices represent 105 recent books sold from Amazon.com

Divide the books according to their political alignment Liberal / Conservative / Centrist

Example

Polarization in the 108th Senate

108th House by Party

108th House by Ideology

108th House by State

108th House by Committee

Polarization Over Time in the House

Polarization Over Time in the Senate

Black Legislators in the 103rd House

Black Legislators in the 104th House

Black Legislators in the 108th House

Poor Districts in the 108th House