Like most of you here, I've kept a watch on Neil Stevens' Swing-O-Meter and his various poll-based projections. (Always a worthwhile read, Neil.) And like many of you, I also have enjoyed watching more and more names mount and shift right on Cook's Political Report. Being a numbers guy myself, I thought it would be fun to create my own gauge for what kind of swing the Republicans might end up with this time around, so I have come up with the 90-50 formula.
We start with the current version of Cook's House Projections. As has been noted before, Cook is notoriously hesitant to shift any race with an incumbent beyond "Toss-Up", which means that when he lists a race as such, there is much more than a 50% chance that the other side is going to win the race. And if you believe what you read from many other sources, many of the "Lean D" races are quite competitive, with some polls indicating a Republican lead. As for the Republican side, Charles Djou's seat is at worst a toss-up for us (recent polls show him leading), and there is no seat that is currently listed as "Lean Republican" that looks like an upset. So we'll leave those out.
So the formula works out like this: 90% of "Democratic Toss-Ups" will shift, 50% of "Lean Democratic" will shift. Add to that any seat that Cook has already placed on the other side, and you have your number.
So let's see what we end up with:
Democrat Toss-Ups: There are currently 46 of them. 46 * 90% = 41.4, so we'll round down and say 41 of these seats shift.
Leans Democrat: 28 Democrat seats fall into this category. 28 * 50% = 14 seats.
R seats leaning D: There are 3 of these (IL-10, DE-AL, and LA-2).
D seats leaning or likely R: There are 17 in the "Lean R" column, and 6 more in the "Likely R" column, for a total of 23.
So to sum it all up:
Leans: + 14
R to D: - 3
D to R: + 23
Total: 75 seats
That seems like a good number to me. Feel free to play along at home when Cook's next report comes out.