SpliteVote% (I) and StraightVote% (S) must each be in [0,1]--

however their interactions can have

Take the following sets:

S: [0.1, 0.2, 0.3]

I: [0.1, 0.2, 0.3]

Slope on S on (I-S) = 0

Now:

S: [0.1, 0.2, 0.3]

I: [0.2, 0.4, 0.6]

Slope on S on (I-S) = 2