Trying to understand Presidential Polls

[Duckus]

I understand how polling works. I understand how margin of error works. And I understand that polls can be useful. I am not an expert in any of this, but I understand it enough I think.

What I can’t understand is the variation in the poll results DAILY. I can understand significant changes over the course of an election as people decide about candidates. But EVERY day I see new polls – Obama up 12, Obama up 8, McCain up 4, Tied, Obama up 2, and so on and so on. Gallup literally had two polls in one day that were 8 points different.

The reason I don’t get these wild swings is I can probably name the amount of people I know who are truly “undecided” about Obama and McCain on one hand. Most people I know are heavily leaning one way or another. I have also some friends who are not going to vote at all, and others who are voting 3rd party. But really no one I know wakes up Monday being excited for Obama then on Wednesday has a McCain bumper sticker and then on Friday is at an Obama rally back on Obamanation.

Is it just me – does everyone else know who the hell these millions upon millions of undecided are? And not just undecided, but daily flip floppers?

The reason I think its important is that polls seem to stir the national debate on the election. Who is doing well. Is one candidate unstoppable? Is some falling? Is someone surging? Etc, Etc? The entire national debate is crafted by something that seems to be no more than a guess.

[PeterMP]

I understand how polling works. I understand how margin of error works. And I understand that polls can be useful. I am not an expert in any of this, but I understand it enough I think.

What I can’t understand is the variation in the poll results DAILY. I can understand significant changes over the course of an election as people decide about candidates. But EVERY day I see new polls – Obama up 12, Obama up 8, McCain up 4, Tied, Obama up 2, and so on and so on. Gallup literally had two polls in one day that were 8 points different.

The reason I don’t get these wild swings is I can probably name the amount of people I know who are truly “undecided” about Obama and McCain on one hand. Most people I know are heavily leaning one way or another. I have also some friends who are not going to vote at all, and others who are voting 3rd party. But really no one I know wakes up Monday being excited for Obama then on Wednesday has a McCain bumper sticker and then on Friday is at an Obama rally back on Obamanation.

Is it just me – does everyone else know who the hell these millions upon millions of undecided are? And not just undecided, but daily flip floppers?

The reason I think its important is that polls seem to stir the national debate on the election. Who is doing well. Is one candidate unstoppable? Is some falling? Is someone surging? Etc, Etc? The entire national debate is crafted by something that seems to be no more than a guess.

Comparing from poll to poll (daily) is very tricky because they have different definitions of "likely" voters, (if that is what they are reporting) which means their over-lap of "good" responders doesn't match up and other "data analysis" they are doing (for the most part, you aren't seeing raw responses).

Just looking within a poll, numbers don't change that much from taking to taking for the most part:

http://www.realclearpolitics.com/epolls/2008/president/us/general_election_mccain_vs_obama-225.html

CNN07/27 - 07/29914 RV5144Obama +7.0

CNN06/26 - 06/29906 RV5045Obama +5.0

CNN06/04 - 06/05921 RV4946Obama +3.0

Rasmussen Tracking07/29 - 07/313000 LV4746Obama +1.0

Rasmussen04/24 - 04/271600 LV4646Tie

FOX News07/22 - 07/23900 RV4140Obama +1.0

FOX News06/17 - 06/18900 RV4541Obama +4.0

FOX News04/28 - 04/29900 RV4346McCain +3.0

NBC News/Wall St. Jrnl07/18 - 07/211003 RV4741Obama +6.0

NBC News/Wall St. Jrnl06/06 - 06/091000 RV4741Obama +6.0

NBC/WSJ04/25 - 04/281006 RV4643Obama +3.0

The only poll, I've seen recently with big movement is this one:

USA Today/Gallup07/25 - 07/27791 LV4549McCain +4.0

USA Today/Gallup06/15 - 06/191310 LV5044Obama +6.0

To look at the USA Today/Gallup and the CNN and be like there is an 11 pt. swing overnight (or even the CNN and Rasmussen and say there has been an 8 pt. swing), isn't a statistically sound thing to do.

I know the press does it like that, but the real question is for that organization(s) how much has the poll moved, and even then, things can be misleading because they don't report what they are doing with the data (what is their defintion of a likely voter) so you can't even be sure that the change wasn't a change in their defintions.

The numbers for registred voters have been pretty solid from organization to organization.

Specifically Gallup does at least two different things. They report regsitered voters (daily tracking) and likely voters (USA Today/Gallup). Cross comparing them w/o considering the differences will result in poor conclusions.

***EDIT***

And even for registered voters things are tricky between organizations. When are they calling (obviously, if you call only in the evening vs. anytime in the day that can affect your respondents)? What are they doing w//about cell phones? How are they asking the question? etc. etc.

Looking across an organization is normally okay, but it is difficult to asses how/if they've changed things a lot of times that might have resulted in a changes in the results.

[Predicto]

Exactly.

To simplify, every pollster gets raw numbers, then "tweaks" those numbers accoring to their own secret formula, to reflect the fact that not everyone who has an opinion will actually vote in November.

(I know you two guys understand that - this was for the benefit of Tailgaters who don't follow the art of polling much...)

Anyhow,I don't know what they are doing at the Gallup Daily Tracking poll, but it is clearly different than what everyone else is doing.

[USS Redskins]

Thats funny, I actually was called yesterday by Gallup at about 6pm. They asked me my age and if I was registered to vote and if I planned on voting in November. Then they said if the election were held today, who would I vote for and gave me the choices of Obama, McCain, Other or undecided.

I was so tempted to be a wise-ass and say something like Homer Simpson but I went with McCain.

First time I have ever been inlcuded in polling. It was very interesting.