Below we use DW-NOMINATE scores updated through the August recess of the 113th Congress to plot the mean first dimension (liberal-conservative) scores of Republicans and Democrats and the difference in these party means over time. Using the difference of party means as a measure of polarization, we find that polarization ticked upwards from 1.09 in the 112th House to 1.11 in the 113th House. This increase is entirely attributable to a change in the House Republican mean from 0.69 to 0.71 on the liberal-conservative dimension. House Democrats in the 112th and 113th Congresses both occupied a mean position of -0.40.
From a long-term perspective, polarization in the House has continued to break records dating back to the large ideological gap between Democrats and Republicans in the early 20th Century House. This of course has important implications for how the House will go about resolving a number of important issues on the agenda in the forthcoming months; namely, Syria, the budget, raising the debt ceiling, immigration reform, and the farm bill.