Here is one of their most prominent graphs.
This graph shows that there is a greater divide between Republicans and Democrats than there was in 1994. It does not show who is responsible for the divide. The rest of the study consistently reiterates that Democrats as well as Republicans are becoming more liberal, and this is causing the ideological split between the two parties.
The conclusion drawn is false. The charts are specifically chosen to avoid showing which party is more responsible for the divide. In fact, the Republicans have caused most of the gap. The Pew results review the opinions of voters as a whole, but the important polarization is in Congress, and there, according to the following chart, the Republicans provide almost the entire gap.
The second chart comes from Polarized America, a book about income disparity, among other things. In the second chart, which provides information on who is changing and how much, we can see that between 1977-79 and 2011-12, the Democrats in Congress have become slightly more liberal, about 0.1 per cent. During the same period, Republicans in Congress have become 0.5 per cent more conservative. The gap between the two parties has been increased primarily by Republicans becoming more conservative, not by Democrats becoming more liberal.
Given the findings in Polarized America, I can only conclude--with Norm Ornstein--that Pew Research is misinterpreting its own findings in a manner that is highly favorable to the Republican Party. This study's erroneous conclusions will give fuel to journalists and scholars who wish to avoid blaming Republicans for the impasse in Congress. This development is similar to the Republican polls that showed Mitt Romney winning "in a landslide" up until the moment that Barack Obama defeated him decisively in the 2012 presidential election, as well as the poll in Eric Cantor's congressional district that showed he had a 34 percentage point lead just two weeks before he lost a decisive primary.
Conservatives should take no comfort in such misleading reports. Their party is rapidly moving away from the center of the electorate, the place where elections are won and lost.