Scott analyzes DW-NOMINATE data which unexpectedly shows no leftward drift in US politics over 120 years, despite historical evidence suggesting otherwise.
Longer summary
Scott Alexander examines the claim that society is drifting to the Left by looking at DW-NOMINATE, a statistical system that analyzes legislators' voting patterns over time. The system shows that while Congress has become more polarized and Republicans have shifted right since 1980, there has been no significant liberal drift in either party over the past 120 years. This result contradicts the expected leftward shift given historical developments like the expansion of the welfare state and civil rights movement. Scott finds this counterintuitive and struggles to explain it, noting that the system is well-regarded and its developers defend its use for intertemporal comparisons.
Shorter summary