Question about the already voteds that I put to Nate Silver of 538

[abumbyanyothername]

Nate:

I don't know how busy you are. I am sure you are quite busy. I have a question about the already voted line in some of these polls.

Diago/Hotline shows the already voteds at 48% Obama/47% McCain. Many other polls show the gap at closer to 20%. What is the reason for this wild divergence? I am sure it must be methodology, but I don't know what is the difference in their reporting. Do you?

Also in the most recent Pew poll that showed Obama leading among already voteds by 19 (http://people-press.org/report/465/mccain-support-declines ), I note that the Obama already voted line dropped 10 points in a week, and McCain's line only went up 2 points in the same period. Plus the Obama + McCain number for the already voteds dropped in the same period from 95 to 87. I tend to believe that somebody at Pew made a mistake on Obama's number, perhaps writing or entering 53 when the actual number is 63. Do you have a view on this?

Thanks in advance.