Paul Sheehan has a piece in today’s SMH on “Red and Blue America”. His conclusion – that American politics is more ideologically polarised today than in the past – is basically right. But he uses the wrong set of facts to show it. Sheehan argues that we can discern polarisation by looking at how many states are “swing states”. But at best, this tells you about geographic polarisation, not ideological polarisation. And at worst, it tells you that when parties devote a larger share of resources to the same set of states, those states are more likely to be swing states.
The only real way to understand polarisation is to look at the ideological positions of members of Congress. Over the years, political scientists Keith Poole and Howard Rosenthal have done just that, categorising bills on a left-right spectrum to give each member of congress an ideological score, and using the fact that members of Congress overlap to rank consistently across multiple years. From 1980 onward, the Republicans have steadily moved to the right, leaving a significant gulf between the two parties (see graphs here).
Perhaps some enterprising political scientist could do the same for Australia?