Karl Rove is Wrong

Today, in the Wall Street Journal, Karl Rove counsels voters not to, "let the polls to affect your vote. They were wrong in 2000 and 2004." There are several things wrong with this, and the most glaring is actually that in the column, Rove writes only about exit polls. His argument is that exit polls can lead to erroneous assumptions about who the winner will be be (that's certainly true, and is especially true of "early exits" of the type that were leaked in 2004).

But the implication of this column is that we can't really trust public opinion polls, so we don't know if Obama is really ahead. This insinuation is popping up all over the place. Take a look at the bottom story on today's msnbc website:


Now, you can probably guess where I'm going with this.

I downloaded electoral-vote.com's entire cache of 2004 polls and then I took a simple average of each state's polling from the last five days of the election. I used a simple average because, unfortunately, the data did not include sample sizes. Here are the results (note that in 16 states there was no public polling in the final five days) :

State	Kerry Avg	Bush Avg
Alabama	42.0	53.0
Arizona	41.0	56.0
Arkansas	44.5	51.0
California	53.5	43.0
Colorado	46.3	48.9
Connecticut	52.0	42.0
Florida	47.3	47.9
Georgia	41.3	54.0
Illinois	53.0	42.0
Indiana	38.0	57.5
Iowa	47.0	46.7
Kentucky	38.0	59.0
Maine	52.0	44.0
Maryland	53.0	43.5
Michigan	48.4	46.1
Minnesota	48.4	45.9
Missouri	45.3	50.3
Nevada	45.4	50.4
New Hampshire	48.3	47.0
New Jersey	48.2	41.5
New Mexico	45.6	49.0
New York	54.3	37.7
North Carolina	44.0	53.0
Ohio	46.7	48.3
Oklahoma	34.0	64.0
Oregon	51.5	45.0
Pennsylvania	48.4	46.4
South Carolina	42.0	54.5
Tennessee	40.0	58.0
Texas	34.5	58.5
Utah	24.0	69.0
Virginia	46.0	50.5
Washington	51.7	45.3
West Virginia	43.0	51.0
Wisconsin	48.2	46.2

Of these 35 states, the polling correctly "predicted" the winner in 34 cases. The only exception is Iowa, where the final average was closest of all the states. Moreover, the average difference between the final margin in the polls and the actual final margin was less than 2.4 points. Indeed, in 21 of these states, the polls "predicted" the margin of victory to within 3 points.

The story is even better when looking only at "swing states." Among the fifteen "showdown states" identified by CNN, the average difference between the final polling margin and the actual margin was less than 1.9 points. In Pennsylvania, for example, the average of the final polls gave Kerry a lead of 2.1 points. The final margin was 2.2 points.

Can polls be wrong? Yes, of course, there is always a chance that individual polls are off base. But when taken together, polls paint an accurate picture. Even a simple averaging of polls yields very reliable results (though I prefer to weight my averages when I have the data to do so). 2004, despite Karl Rove's ominous column, is great evidence of that.