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Different Polls, Different Trends

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As the discussion of Charles Franklin's column on house effects suggests, most people believe that "who's right" in their poll results these days will be resolved after Election Day. Then we can compare which polls came closest to the final results, and infer that the most accurate polls in the final pre-election predictions were probably the most accurate during the campaign as well.

 

But it doesn't usually work out that way. In 2004, the seven polls noted in the accompanying chart all showed Bush winning by a margin of one to three percentage points, except for Fox, showing Kerry the winner by two. All the results were well within the polls' margins of errors in comparison with the actual election results.

 

0810_14 Final Poll Predictions 2004 Election.png

However, the interesting point is that during the month of September, these very same polls showed dramatically different dynamics. As shown in the next graph, there were three basic stories: ABC, Gallup, Time and ABC all showed Bush gaining momentum in the weeks following the Republican National Convention, and then falling toward the end of the month. Furthermore, although these pollsters all agreed with the general pattern, at the end of the month Gallup showed Bush with an 8-point lead, CBS and Time had him at one point, and ABC at 6 points.

 

The second story, reported by Fox, Zogby and TIPP, showed very little movement over the month of September, with the margin varying from a Kerry lead of one point to a Bush lead of three points.

 

Finally, Pew had its own dynamic, not found by any of the other polls, showing a significant surge for Bush after the convention, followed by a dramatic decline, then another significant surge.

 

0810_14 Bush Lead Sept 2004.png

One of the most interesting comparisons is between Gallup and Pew, which diverged by 13 points in mid-September, but closed to agreement by the end of the month.

 

At the end, all the pollsters could claim they were "right" on target, and NCPP dutifully noted the fine performance of the media polls. That performance, of course, was only in the final prediction. No effort was made to evaluate the polls during the campaign, though clearly they presented contradictory results. It appears as though we need a means of evaluating the polls during the election campaign.

 

It's true, of course, that we can't know which polls are most accurate during the campaign, but we can say that collectively they often tell quite divergent stories. And that hardly qualifies them for plaudits after Election Day.

Last week (Oct. 6), Gallup and DailyKos/Research 2000 tracking polls both showed Obama up by 9 and 11 points respectively, the same figures they show as of Oct. 13. Diageo/Hotline, GWU/Battleground and Zogby tracking polls all showed quite different results - with quite different trends.

 

On Oct. 7, Diageo/Hotline, GWU and Zogby showed an average of a 2-point lead for Obama, while DailyKos and Gallup showed an average of a 10.5 point lead. All three of the former polls reported an increasing lead for Obama in the subsequent week, while Gallup and DailyKos told us there was essentially no change.

 

Obama's Lead Among Five Tracking Polls

 

Gallup

Gallup2

DailyKos

Diageo

GWU

Zogby

6-Oct

9

 

11

2

7

3

7-Oct

11

 

10

1

4

2

8-Oct

11

 

10

6

3

4

9-Oct

10

 

12

7

8

5

10-Oct

9

 

12

10

 

4

11-Oct

7

6

13

8

 

6

12-Oct

10

10

12

6

8

4

13-Oct

9

10

11

6

13

6

 

 

After the election, will we know which tracking polls were right? If history is a guide, all will come within their polls' margins of errors compared to the final election results. And we will all forget how confusing their different prognostications were during the campaign.

 

Perhaps we need another standard by which to judge the polls' performances during the election campaign.

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