I've dug up a couple more states and modified my rounding rules to be consistent. Most of the PVI's reported are in whole numbers so a D+5.2 = D+5. I'll round the PVI to the nearest percent before using it to determine the status of a district. That matters for instance in IL where 3 districts are between D+5.0 and D+5.5.
I can also measure the swing seat composition of a map with a similar technique. Add half the lean districts (PVI 2-5) to the even seats (PVI 0-1) to get a total. The swing seat factor (SSF) is the square of that total should be roughly equal to the number of districts in the state if the map has neither too few nor too many swing districts.
IL (18): Partisan Difference D+6, Partisan Bias 25.6%, PBF 21.2, Swing seats 4, SSF 16.
NJ (12): PD D+2.5, PBI 16.4%, PBF 3.9, Swing seats 2.5, SSF 6.
PA (18): PD R+4.5, PBI 27.0%, PBF 23.6, Swing seats 4.5, SSF 20.
WA (10): PD D+1, PBI 5.0%, PBF 0.3, Swing seats 3, SSF 9.
What this would suggest is that IL and PA are partisan gerrymanders, and NJ is fair but leans towards incumbent protection. WA passes this partisan test, though it could have other problems on purely geographical factors like county integrity.
How would this work with Massachusetts and its 0 swing seats?
As I understand it these are the Massachusetts PVIs.
1: D+14
2: D+12
3: D+8
4: D+11
5: D+15
6: D+6
7: D+30
8: D+8
9: D+7
