Has income inequality or media fragmentation increased political polarization?

The increasing polarization of Congressional voting patterns has been attributed to factors including generational shifts, economic conditions, increased media fragmentation, and greater income inequality. The first of these factors is difficult to test with time series data owing to the low frequency of generational shifts, while the tendency of business cycles to reverse suggests that economic cycles are unable to account for long-term shifts in polarization. This leaves two main possible long-run drivers: the increasingly fragmented state of American media as stressed by Prior (2005, 2007) and Duca and Saving (2012a), and increased income inequality, as emphasized by McCarty, Poole, and Rosenthal (2006, forthcoming) and Stiglitz (2012). ; Using statistical techniques suitable for analyzing variables with shifting long-run averages we find evidence indicating that media fragmentation has played a more important role than inequality, at least as tracked by available data and measures. Periods when the share of Americans with access to cable or satellite TV has risen are followed by upward shifts in polarization. Furthermore, our results suggest that the polarization arising from media fragmentation or inequality may make it more difficult to achieve the political consensus needed to address major challenges, such as the long-run fiscal imbalances facing the United States.