May 3, 2008
POLL: Zogby IN, NC (5/1-2)
Zogby Tracking (release)
Indiana
Obama 43, Clinton 42
North Carolina
Obama 46, Clinton 37
By Eric Dienstfrey on May 3, 2008 9:10 AM | Permalink | Comments (42) | TrackBacks (0)
April 27, 2008 - May 3, 2008
May 2, 2008
POLL: InsiderAdvantage IN (4/30-5/1), NC (5/1)
North Carolina
n=611
Obama 49, Clinton 44
Indiana
Clinton 47, Obama 40
Note: InsiderAdvantage's 4/29 survey showed African Americans at 25% of likely Democratic primary voters in North Carolina, while their 5/1 survey shows it at 33%.
By Eric Dienstfrey on May 2, 2008 5:00 PM | Permalink | Comments (19) | TrackBacks (0)
POLL: Daily Tracking (through 5/1)
Gallup Poll
National
Clinton 48, Obama 46
McCain 48, Obama 42... McCain 46, Clinton 45
Also
"Clinton's vs. Obama's Strengths in the General Election"
Rasmussen Reports
National
Clinton 46, Obama 44
McCain 48, Obama 42... McCain 45, Clinton 44
Favorable / Unfavorable
McCain: 52 / 44
Clinton: 46 / 52
Obama: 49 / 48
New Hampshire
McCain 51, Obama 41... McCain 47, Clinton 44
Sen: Shaheen 51, Sununu 43
New York
Obama 52, McCain 35... Clinton 60, McCain 31
Also
"58% Say Obama Denounced Wright for Political Convenience, not Outrage"
By Eric Dienstfrey on May 2, 2008 1:40 PM | Permalink | Comments (13) | TrackBacks (0)
North Carolina: Trend Sensitivity
Time for another update looking at the "sensitivity" of our trend lines for North Carolina. As Professor Franklin is tied up with his day job this morning, I will be your guide. But let's go immediately to the chart that Franklin just generated.
The solid red and blue lines represent our standard trend estimates of support for Barack Obama and Hillary Clinton, respectively, in North Carolina. The trend lines are based, not on simple averaging, but on a local-regression based trend. We deliberately set the standard estimate to be conservative in that it takes a good bit of evidence of "real" change (i.e. more than one or two contrary polls) before the trend will show a sharp turn. As we have noted before, with lots of polls, this more conservative estimator has an excellent track record of finding real turning points of opinion while not chasing outliers.
In this case, however, the standard line appears to be too conservative. The last nine polls have produced results below the solid trend line for Obama and all but one above the trend line for Clinton. So in the graph above, we have also included trend lines based on a more sensitive estimator -- the dotted lines -- for both candidates. The sensitive estimator uses the same local regression methodology as our standard approach, but sets the degree of smoothing to about half that of the standard blue estimator. The sensitive estimator should detect short term change more quickly than "blue", but it will also sometimes chase phantom changes due to flukes of a few polls that happen to be too high or too low.
In this case, for the moment at least, the sensitive estimator (which shows Obama leading by a 7.7 point margin or 50.3 to 42.6) fits the most recent data better than the standard estimate (which shows Obama leading by 13.7, or 52.7 to 39.0).
Update: In the hour since Charles generated this chart, we have added new polls from Rasmussen Reports and ARG that change the numbers for the standard estimates on on our North Carolina chart slightly from what appears in the graph above. We'll try to post an update of the more sensitive estimate trend later this afternoon.
By Mark Blumenthal on May 2, 2008 12:18 PM | Permalink | Comments (0)
POLL: ARG Indiana, North Carolina (4/30-5/1)
American Research Group
Indiana
n=600
Clinton 53, Obama 44
North Carolina
n=600
Obama 52, Clinton 41
By Eric Dienstfrey on May 2, 2008 12:06 PM | Permalink | Comments (9) | TrackBacks (0)
POLL: Rasmussen North Carolina (5/1)
Rasmussen Reports
North Carolina
n=831
Obama 49, Clinton 40
By Eric Dienstfrey on May 2, 2008 11:34 AM | Permalink | Comments (9) | TrackBacks (0)
POLL: Downs Center Indiana (4/28-30)
Downs Center/SurveyUSA
(Pres release, Gov release, Crosstabs)
Indiana
Clinton 52, Obama 45 (n=689)
n=1,274
Obama 48, McCain 47... Clinton 48, McCain 45
More information on the Downs Center/SurveyUSA methodology.
By Eric Dienstfrey on May 2, 2008 11:06 AM | Permalink | Comments (5) | TrackBacks (0)
POLL: Zogby Indiana, North Carolina (4/30-5/1)
Zogby
North Carolina
n=668
Obama 50, Clinton 34
Indiana
n=680
Obama 42, Clinton 42
By Eric Dienstfrey on May 2, 2008 10:45 AM | Permalink | Comments (14) | TrackBacks (0)
May 1, 2008
POLL: Research 2000 North Carolina (4/29-30)
Research 2000
North Carolina
n=500
Obama 51, Clinton 44
By Eric Dienstfrey on May 1, 2008 5:55 PM | Permalink | Comments (7) | TrackBacks (0)
POLL: CNN National (4/28-30)
CNN/ORC
National
441 registered Democrats and those who lean Democratic
Obama 46, Clinton 45
Obama 49, McCain 45... Clinton 49, McCain 44
By Eric Dienstfrey on May 1, 2008 5:08 PM | Permalink | Comments (4) | TrackBacks (0)
Predictive Accuracy of the 2008 Pennsylvania Primary Pollsters
Berwood Yost is Director of The Floyd Institute's Center for Opinion Research at Franklin & Marshall College. Kirk Miller is B.F. Fackenthal Professor of Biology and Senior Research Fellow at The Floyd Institute's Center for Opinion Research.
The 2008 Democratic presidential primary on April 22 put Pennsylvania in the national spotlight for a long six weeks. Members of the media followed the candidates into the Keystone State intending to learn more about its people and its politics. Not far behind the media came the pollsters--some media even brought their own pollsters. Pennsylvania voters were besieged by pollsters in unprecedented numbers. There were 39 publicly released surveys, which included more than 30,000 interviews with the state's voters, during only the last three weeks of the campaign. This is a tremendous increase in polling activity compared to the 26 polls released in the final three weeks of the 2004 presidential campaign in Pennsylvania or the 15 released during the final three weeks of the 2006 Senate campaign.
Taken together, the pollsters who pestered Pennsylvanians did an adequate job of predicting the final outcome: 36 of the 39 polls in April predicted a Clinton victory and the three outliers were all conducted by the same polling organization. We agree with Charles Franklin's assessment that the aggregate performance of the Pennsylvania pollsters was good. Figure 1 is a frequency distribution of the predictive accuracy of the 39 public polls released in Pennsylvania. It shows that there was a slight bias in the polling estimates toward Barack Obama (meaning the polls in Pennsylvania underestimated Hillary Clinton's margin of victory), but that this bias was small and, according to the exit polls, not surprising because late deciding voters moved in larger proportions toward Clinton.
Figure 1 Frequency Distribution of Predictive Accuracy
Some individual pollsters faired much better than others in the accuracy of their estimates. Figure 2 shows the predictive accuracy and corresponding confidence interval for each of the 39 polls conducted between April 1 and 22 in Pennsylvania, arranged by the number of days prior to the primary the survey was completed. Those pollsters who produced a biased estimate, meaning the confidence interval for their estimate did not overlap zero, are labeled in Figure 2. Three of the four polls conducted by Public Policy Polling (PPP) were biased and all were biased toward Obama. Two of the three polls conducted by American Research Group (ARG) were biased and one of SurveyUSA's three polls showed bias. One ARG poll showed that Clinton and Obama were tied; the other, seven days later, showed Senator Clinton ahead by 20 points. The SurveyUSA poll that missed also showed Senator Clinton ahead by 20 points. The measure of predictive accuracy we used shows that the pollsters' final estimates were mostly in line with the final election results.
Figure 2 Predictive Accuracy of Individual Polls by Date of Poll
The misses identified in Figure 2 are not related to sample size. Four of the surveys that missed had four of the eight largest samples; the other two that missed had sample sizes that were only slightly below the median size. There is a relationship in these analyses, as one would expect, between sample size and the widths of the confidence intervals, but there is no relationship between sample size, width of the confidence interval, and the likelihood that a survey was biased. We don't know what methodological choices matter most in producing unbiased polls without further examination of the methodological choices the pollsters make. Some might conclude that pollsters who use inter-active voice response (IVR) technology to collect data are more prone to bias because two of the three pollsters who produced biased estimates use IVR, but not all IVR pollsters produced biased results.
Another interesting question we tried to answer is whether the polls converged on the end result as election day approached. Depending on the method used, the answer is a qualified, "slightly." Figure 3 shows the predictive accuracy of each poll as a function of days before the Pennsylvania primary. The trend line fitted to the figure is produced by a LOWESS iterative locally weighted least squares regression. The red dots identify the six biased polls noted earlier. The curve indicates that the polls began to converge until about two weeks prior to the election, that they remained relatively constant for about a one-week period, and then began to converge again over the final days of the campaign. If the six biased polls are removed from the analysis, the convergence is not dramatically improved.
Figure 3 Predictive Accuracy of Individual Polls by Date of Poll with Fitted Regression Line
Measuring Predictive Accuracy
We used the measure of predictive accuracy developed by Martin, Traugott and Kennedy (2005) A Review and Proposal for a new Measure of Poll Accuracy. Public Opinion Quarterly, Volume 69 (3): 342 - 369. Their method compares the ratio of the estimated percent of voters voting for each candidate to the ratio of the final vote tally for each. The natural log of this odds ratio (ln odds) is used because of its favorable statistical properties and the ease of calculating confidence intervals for each estimate. The confidence interval for a poll that reasonably predicts the final outcome of the primary election will overlap zero. Senator Clinton's votes or projected votes were the numerators in all the ratios we calculated so negative values for ln odds represent an overestimate in favor of Senator Obama and positive values represent an overestimate in favor of Senator Clinton. According to this measure, a poll is biased if its confidence interval does not overlap zero. The polling results used in this analysis were taken from