Friday, September 19, 2008

Are you interested in polls and what they mean? Here's some very instructive information.

If you're at all interested in what the hell the polls mean, here is one explanation, from a friend of mine who works in a polling group, when I asked what MoE, margin of error, means. Even I understood it. If you're interested in more explanations, leave me a comment and I'll follow up. Here it is:

MoE is Margin of error. So 293 with a MoE of 45 means it could be as little as 270.5 and as much as 315.5. (NOTE: 315.5 - 270.5 = 45, the MoE). Obama has a margin of error range of 315.5 to 270.5 with 293 (the middle of the range) being the most likely.

OK, ignore that fact that you cannot get a 1/2 vote.

The total EV is 538. So if Obama has 293, then that leaves 245 for everyone else.

No 3rd party candidate is even close to getting anything other than 0 so McCain winds up with the remaining 245.

So this is why we say:

Obama: 293 (middle of the MoE range) McCain: 245 (everything else) Others: 0 (nothing even close) with a MoE of 45.

What does that mean in terms of chances of winning? Well ...

The actual vote will lie within the MoE range (315.5 to 270.5) 75% of the time. This means 25% of the time we are outside the margin going either higher or lower than the MoE range. When the election is this close you can think that 1/2 of those "outside the margin" casses or 12.5% of the time the vote will be above the MoE range. So 12.5% of the time Obama could get more than 315.5 EV.

The same goes for below the MoE range. So 12.5% of the times Obama could get less than 270.5 EV.

This is not exactly the case. The above MoE case is a little less than 12.5%. The below the MoE case is a little more than 12.5%. However for a race that is not a land slide, splitting the 25% into two equal parts for above and below the MoE range is a good enough approximation.

Back to the "good enough approximation":

So 12.5% of the time, it could be higher than 315.5 (Obama wins by an even bigger margin then we expect) and 12.5% of the time it could be lower than 270.5.

Obviously, if it is higher than 315.5 Obama still wins. What about the below the MoE case? Well, Obama has a narrow win at 270. At 269 there is a tie.

What happens if it is a 269 to 269 tie? When no candidate has 270- votes, the selection of the President is made by the house and the selection of the Vice Preside is made by the senate picked from the CURRENT 110th congress membership. Assume that house and senate members vote along party lines.

In the senate each member has 1 vote. Voting along party lines means that Biden would be selected VP, winning by 1 vote.

In the house each state casts 1 vote. States where the membership is split 50/50 would be unable to vote and would cast present (voting for none). For example AZ 8 house members are split 4 D's and 4 R's. McCain's home state would not be able to vote for him. So if the Presidential election where thrown into House and members vote along party lines, Obama wins by 9 votes (with two states AZ and KS not voting for any candidate).

So Obama and Biden both win on a 269-269 tie with McCain.

Anything at or below 268 for Obama and McCain wins.

Now you need 270 to win, so with Obama at 293 with a 45 MoE, we mean that he has slightly better than 87.5% chance of winning IF the election were held today. (Sept. 19)

When you bring in a number of minor technical factors (2nd order effects), the 87.5% win chance becomes about 87.8%.


So when you lead by the MoE, about 7 out of 8 times you will win.

It turns out that when you lead by 1/2 the MoE you will win about 2 out of 3 times.

And when you lead by twice the MoE you will win about 19 times out of 20

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