https://fivethirtyeight.com/features/the-two-cracks-in-the-r...
http://www.pewresearch.org/fact-tank/2014/06/12/polarized-po...
https://twitter.com/gelliottmorris/status/888904322326638592
Liberals are at 0.38, and the most extreme they've ever been was 0.39. They have been somewhat more liberal than they were in the 40s, but they've generally been within the same band of scores for the last 100+ years.
Conservatives, on the other hand, are at 0.49, which is the most conservative they've been in the last 200 years. They've basically doubled since the 1970s.
So, objectively, conservatives are more extreme (0.49) than liberals (0.38) today. Also, the most extreme conservatives are more extreme than the most extreme liberals.
https://en.wikipedia.org/wiki/NOMINATE_(scaling_method)
I think this may be the first time I've seen this, but I'm quite confused about the claim to be able to make comparisons across time by simple statistical methods. The model has a clear statistical meaning about the similarity of different members of the same Congress, who have all voted on the same set of questions. But surely the issues that the Congress is actually voting on are radically different from decade to decade? Slavery, the Federal income tax, alcohol prohibition, the New Deal?