Explaining "The Breakdown"

I got an email asking me to explain the numbers in "The Breakdown" a bit more clearly. The numbers there are intended to show the approximate range of likely outcomes if the election were held today. The top line shows the best case for Obama, the second line shows the same for McCain. To arrive at these numbers, I simply take all states that are tied or are polling at less than 5% in the favor of a candidate and switch their side.

For example, today there are two states that are tied, PA and VA for a total of 34 EVs. There are four states that are supporting McCain by less than 5%, Ohio, Indiana, New Mexico and Nevada, for a total of 41 EVs. So Obama's best case number for today is all the states that are currently polling in his favor (247 EVs) plus 34 ties plus 41 McCain leaners for a grand total of 322 EVs. The worst case numbers are simply the number of EVs that a candidate has that are polling at a 5% or higher margin. If I did my math right (never guaranteed!) those two numbers should always add up to 538.

The final two lines in the table list the changes since yesterday and since seven days ago and are based on their best case number. Since these numbers are affected by the strength of support, not just leaners, these two numbers won't always match up. For example, over the last week Obama has lost more strength than McCain has gained. That is because at some point in the last week one or more states have increased their support of McCain to the point where they crossed that 5% threshold. McCain's numbers don't change under that circumstance, but Obama's do.