Sorry for a disorganised comment, but here’s a recent summary I’ve wrote about why most people, including academics, are wrong about polarisation (ping me for references and details): There’s been a lot of high quality research on polarisation since at least the 80s, spearheaded by Keith Poole and Howard Rosenthal. Around the time of Trump’s election, the subject became extremely popular and a lot of people (including me) decided to research this issue. Unfortunately, many of those scholars (including political scientists unfamiliar with polarisation research) believe things that seem to make sense intuitively but that contradict the large body of pre-existing research on polarisation. Findings in the area have established that many seemingly likely causes of polarisation are not causes of polarisation; including polarisation of the electorate, party leadership, polarisation over social issues, and gerrymandering. It seems most people (including academics) can get away with claiming these were the main causes, it seems to be a very common belief (I thought it myself until I fact-checked this); alas, it’s well-established it’s just not so. The only mildly well-established likely cause is economic inequality. It is the only trend that follows the pattern of raising polarisation; but it’s an open question whether there’s an actual causal link from inequality to polarisation. Another plausible contender is polarisation of partisans (people heavily involved in politics), but experts seem split over this issue. It is my impression that the latest research favours the view that this was not a relevant cause and that party sorting better explains the data used in favour of partisan polarisation. The NOMINATE-type measures are the most frequently cited basic data supporting the view that Republicans are now more extremists than they ever wore in the last century. But it does not really directly support this view on its own. NOMINATE-type measures are strictly relational, that is, they measure how far things are from each other, not how far they are from an absolute point such as the centre. Therefore, the data is just as compatible with Republicans moving away from the centre as it is with the whole thing (Republicans and Democrats) moving towards conservatism as part of a long-term macro-trend that changed the US Party System. Nolan McCarty (Poole’s most frequent recent co-author) agreed this is the case by email, but that he believes Republicans drove the trend due to contextual reasons (e.g. Gingrichism, I assume).
Sorry for a disorganised comment, but here’s a recent summary I’ve wrote about why most people, including academics, are wrong about polarisation (ping me for references and details):
There’s been a lot of high quality research on polarisation since at least the 80s, spearheaded by Keith Poole and Howard Rosenthal. Around the time of Trump’s election, the subject became extremely popular and a lot of people (including me) decided to research this issue. Unfortunately, many of those scholars (including political scientists unfamiliar with polarisation research) believe things that seem to make sense intuitively but that contradict the large body of pre-existing research on polarisation.
Findings in the area have established that many seemingly likely causes of polarisation are not causes of polarisation; including polarisation of the electorate, party leadership, polarisation over social issues, and gerrymandering. It seems most people (including academics) can get away with claiming these were the main causes, it seems to be a very common belief (I thought it myself until I fact-checked this); alas, it’s well-established it’s just not so. The only mildly well-established likely cause is economic inequality. It is the only trend that follows the pattern of raising polarisation; but it’s an open question whether there’s an actual causal link from inequality to polarisation. Another plausible contender is polarisation of partisans (people heavily involved in politics), but experts seem split over this issue. It is my impression that the latest research favours the view that this was not a relevant cause and that party sorting better explains the data used in favour of partisan polarisation.
The NOMINATE-type measures are the most frequently cited basic data supporting the view that Republicans are now more extremists than they ever wore in the last century. But it does not really directly support this view on its own. NOMINATE-type measures are strictly relational, that is, they measure how far things are from each other, not how far they are from an absolute point such as the centre. Therefore, the data is just as compatible with Republicans moving away from the centre as it is with the whole thing (Republicans and Democrats) moving towards conservatism as part of a long-term macro-trend that changed the US Party System. Nolan McCarty (Poole’s most frequent recent co-author) agreed this is the case by email, but that he believes Republicans drove the trend due to contextual reasons (e.g. Gingrichism, I assume).