Further, I think the Pew stuff is flawed in a number of ways. One, it comes after the Reagan era, missing a time DW-NOMINATE shows as important to right-wing polarization. Two, it doesn't include the Trump era, when polarization hugely spiked. Third, and most important, 9 out of the 10 questions are not suited for directly measuring ideology. The one I think is actually a decent measure of ideology is "Homosexuality should be discouraged by society" vs "Homosexuality should be accepted by society". The rest of them are practical questions relative to the circumstances of the day. E.g., "The government today can't afford to do much more to help the needy" is a question that's explicitly about the current state of the budget. If the budget improves, then more people should answer that as yes regardless of ideology.
The measure I'd rather see is the extent of ideological litmus tests for access to power. E.g., look at the way the right's orthodoxy on abortion has hardened over the years. In the 1970s it was possible to be a pro-choice Republican and a pro-choice evangelical Christian. Now neither is acceptable, so much so that the most prominent Republican pro-choice group just gave up a few years back: https://www.nytimes.com/2018/06/24/opinion/abortion-rights-r...
Or you could look at the way large portions of the Republican party have polarized around things that are provably false, like that Trump won the 2020 election, that January 6th was a left-wing false flag, or that ivermetcin is a good way to treat covid. That is wildly asymmetrical polarization, and it drove litmus tests for Republican candidates across the country. Nothing similar exists on the left.
DW-NOMINATE didn't create the buckets "far-left", "left", etc. DW-NOMINATE is just a method of marking plots on a graph [1]. The categories of far-left, left, etc. come from drawing boundaries on that graph and giving everyone inside that region a label. Where to draw these boundaries hugely influences the results. Give someone else task of defining the boundaries and you can easily achieve the completely opposite result: like gerrymandering, you can define boundaries on the DW-NOMINATE chart to fit your desired outcome.
Furthermore, there's only 535 members of Congress, out of 300+ million Americans. DW-NOMINATE only examines a very very narrow segment of the population.
By comparison, the Pew survey was based on directly asking people their positions on various issues and measuring political uniformity. This didn't involve the highly subjective task of drawing regions on a chart and deciding these people are center left, these people are far left, etc. Instead it examined how likely people were to have uniform versus heterodox views. It also didn't exclusively study on politicians, it used representative sampling of the general population.
I think it's pretty funny you're acting like looking at the unrandom sample of elected officials is worse than grabbing assorted randos when trying to study politics. It's even funnier that you're taking people's off-the-cuff opinions given to a stranger stranger more seriously than you're taking the actual political behavior of passing laws. Believe what you like, I suppose, but I have a hard time taking you seriously here.
Pew is one of, if not the most respected polling organization in the US. By comparison, that XKCD chart is all just someone drawing boundaries on a chart. Just make the far left zone larger and shrink the far-right zone and voila you have the opposite result.
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