Probability density functions of same-party and cross-party pairs over time.

<p>Probability density functions of the number of roll call vote agreements between pairs of the same-party (SP) and those pairs of cross-party (CP) pairs. The plots show the steady divergence of CPs and SP agreement rates over time. Above each distribution is the Congress number (81–112), followed by the year the Congress commenced, and the number of total roll call votes during the two sessions of each Congress. Pairs with few agreements (below the local minima of a consistently- increasing CP distribution), including representatives from Washington D.C., Puerto Rico are removed.