Today's Polls: No, It's (Still) Not Tightening, by Nate Silver

[jefferson_dem]

Today's Polls: No, It's (Still) Not Tightening

Man, I thought I trained you guys better than this.

There is a lot of consternation in my e-mail box about two polls. One, from Mason-Dixon, shows John McCain just 4 points down in Pennsylvania. The other, from FOX News, shows McCain down just 3 points nationwide.

Let's start with the Pennsylvania result. Mason-Dixon is a pretty strong pollster. So, however, are many others from among the literally dozen or so agencies that have conducted polling within Pennsylvania over the past 72 hours. And none of those other pollsters shows the race that tight.

Mason-Dixon has also had a Republican "lean" this cycle of perhaps 2-3 points. They are quite frequently the most favorable number for John McCain in any given state. That doesn't mean that they are "biased", and it doesn't mean that they are wrong – there are many different (and legitimate!) ways to think about this election. But it does mean that their polls need to be interpreted in that context. Let's say the average poll in Pennsylvania has Obama ahead by 9.5 points. Mason-Dixon will probably start out seeing a 9.5-point state at a 7-point state. If they then end up toward the McCain side of their margin of error -- and they don't use huge sample sizes – that’s how you get to Obama +4.

Now, look. I don't think we need to be in the habit of ripping a poll apart every time that we don't like the result. There is nothing inherently "wrong" with this poll. It's simply that we need to look at in concert with the rest of the evidence. In this case, we have an abundance of evidence, and it suggests on balance that Pennsylvania is neither particularly close, nor is it particularly "tightening" (Mason-Dixon's prior poll of the state, in Mid-September, had Obama up by 2).

It might also help to come at this from the other direction. Here is one poll out of many, out of one "must-win" state out of many, that shows that John McCain is sorta kinda close? This is the best news he can muster? On Monday, I laid out specific criteria for what I'd want to see in order to conclude that the race has tightened materially:

John McCain polling within 2 points in 2 or more non-partisan polls ... in at least 2 out of the 3 following states: Colorado, Virginia, Pennsylvania.

We have yet to see any such results in any of these three states.

<snip>

http://blogs.tnr.com/tnr/blogs/the_plank/archive/2008/10/30/today-s-polls-no-it-s-still-not-tightening.aspx

[BlooInBloo]

1. I was gonna post this with the first fucking sentence as subject.

:P

[HughMoran]

2. Good reading

I like calm and logical explanations.

[NRaleighLiberal]

3. Thanks for posting - you beat me to it! I can't go to sleep without reading this each PM!

[4lbs]

4. Worrying about poll numbers doesn't do anyone any good except the makers of antacids and Rogaine.

n/t

[DerekJ]

5. I like his reasoning ... k&r

[abumbyanyothername]

6. I wish Nate would

give us some insight into the polls that are polling and reporting on the Already Voteds.

He did suggest asking people if they have already voted as a sanity check on likely voter models.

The wild divergence of numbers being reported on this line is driving me crazy! (NYT/CBS = +20; Pew = +19; Diageo = -1; etc.)