Prediction Time

In the Senate, I'm predicting a 7-seat gain for the GOP. Ignoring the seats with 10-point leads one way or the other, there are 8 seats in play, with 2 locked up for the GOP. Those 8 seats are: California (DEM+3), Colorado (GOP+4), Illinois (GOP+2), Nevada (GOP+4), Pennsylvania (GOP+5), Washington (GOP+1), West Virginia (DEM+3), and Wisconsin (GOP+7), where I'm giving the latest poll results in each case. Many of these polls are within the margin of error, but we can still calculate probabilities for each. Based on these numbers, we can find a joint probability distribution for various levels of GOP pickup.

GOP Gain	Probability
+2	negligible
+3	0.04%
+4	0.6%
+5	4.6%
+6	17.6%
+7	34.1%
+8	30.9%
+9	10.9%
+10	1.3%

The median of the distribution is at the high end of a 7-seat GOP pickup. It's certainly pretty likely that we'll have an 8-seat pickup, but playing the odds I'll predict +7.

In the House, it's more complicated since there are a lot more races. Also, polls are sketchier. But let's use the latest Real Clear Politics map to make some estimates. If we plug in some reasonable probabilities corresponding to "likely GOP", "leaning GOP" and "tossup", we get this distribution for GOP seats (here I'm ignoring insignificant tails):

GOP Seats	GOP Lead	Probability
Under 223		0.07%
223	10	0.06%
224	12	0.10%
225	14	0.17%
226	16	0.28%
227	18	0.45%
228	20	0.69%
229	22	1.01%
230	24	1.45%
231	26	1.99%
232	28	2.65%
233	30	3.40%
234	32	4.22%
235	34	5.06%
236	36	5.86%
237	38	6.55%
238	40	7.07%
239	42	7.38%
240	44	7.44%
241	46	7.24%
242	48	6.80%
243	50	6.18%
244	52	5.41%
245	54	4.58%
246	56	3.74%
247	58	2.95%
248	60	2.25%
249	62	1.65%
250	64	1.17%
251	66	0.80%
252	68	0.53%
253	70	0.34%
254	72	0.21%
255	74	0.12%
256	76	0.07%
Over 256		0.08%

The median of the distribution is for the GOP to have 240 seats, representing a 61-seat GOP pickup. There is a 96% chance the GOP will pick up between 50 and 76 seats, and a 90% chance they pick up between 52 and 69 seats. So I think we can count on the GOP having at least a 26-seat majority and it's not impossible for them to attain a 60-seat majority.

Of course, this will do them little good without the Senate or the White House. Those will have to wait until 2012.