For all 50 States + DC,

define partisan lean as

State Margin - National Margin

Then compare the 2020 Partisan Lean to the 2024 Partisan Lean and find the standard error (root mean squared error).

This market resolves to that times 10 (or 100% if >10%).

Roughly accurate numbers

2016 to 2020:

1.6%

2012 to 2016:

3.8%

2008 to 2012:

2.3%

2004 to 2008:

3.7%

2000 to 2004:

2.4%

1996 to 2000:

3.5%

1992 to 1996:

3.3%

1988 to 1992:

3.8%

1984 to 1988:

3.1%

1980 to 1984:

4.8%

1976 to 1980:

4.6%