Polling Trends in 2008 vs '04 and '00

The most common description of polls is that they are snapshots, not predictions. A good way to look at that in the 2008 election is to compare the '08 campaign with the two that came before.

The chart above shows the trend estimates for each of the last three presidential campaigns. I'm plotting the estimated margin between the two candidates, Dem minus Rep, for each year.

With 93 days to go until the 2008 election, Obama holds a 3.3 point advantage over McCain, though that has been eroding over the past six weeks. If we put a confidence interval around today's estimate, we get a race that is just barely leaning Democratic.

But what about the future? The dynamics of the next 92 days are all important for where we stand on November 4. Since we can't foresee those 92 days yet, let's see what happened during the same time in 2000 and 2004. That gives us a better idea how much change we might anticipate in the next three months.

In 2004, Kerry slowly built a 2 point lead by this time, and held a small lead through much of the summer. But then the race took a sharp turn, with Bush making a 6 point run, taking a four point lead with 50 days to go. Kerry gained back 3 points of that in the polling, but less than 2 points of it in the actual vote, losing by a 2.4 point margin.

In 2000, Bush led in most of the early polls, holding a 6 point lead with 107 days to go. Then Gore moved sharply up, erasing Bush's lead and then adding a 3 point lead for Gore with about 56 days left. Bush promptly reversed Gore's gains with a six point move in the GOP's direction, and led by about 3 points over the last three weeks of the campaign. Of course, the 2000 polls were misleading in predicting a Bush win. Gore won the popular vote by 0.6 points.

So far in 2008, Obama has enjoyed a run up of 5.5 points since his low point in late March. That run is on a par with Bush's in 2004 but still a bit less than Gore's 9 point run in 2000, and on par the Bush's 6 point rebound that year.

Judging from the dynamics we've seen in the past it is quite reasonable to expect the current trend to shift by half-a-dozen points. August and the conventions have been periods of substantial change in both previous elections, so if history repeats itself the next 4 or 5 weeks should be pretty interesting.

The bottom line is neither campaign should be complacent or despondent. There is a lot of time left and recent history shows that both up and down swings of 6-9 points are entirely plausible.


As a P.S. here are the three campaigns with educational confidence intervals around them.























The current 2008 estimate is just barely inside the "lean Dem" range, and will move to toss up if the current trend continues for another couple or three polls.

The 2004 estimate was pretty close to the outcome which was well within the 68% confidence interval around the trend.

The polls in 2000 were troubling for having the wrong popular vote winner, but even there the outcome was inside the 95% confidence interval. With races as close as the last two, it is worth appreciating just how wide those confidence intervals are.

Our efforts to characterize races rely on the best estimates of those confidence intervals, but it is all too easy to focus on who's ahead and not remember how much uncertainty there is. That uncertainty is both about where the current estimate says the race stands today and about how the race may change in coming weeks. The data here show that unless one candidate builds a bigger lead than either has held so far, the uncertainty remains pretty big.


Note: My trend here is slightly different from the Pollster National trend because I'm working off the difference between candidates, not each trend separately, and because I've made 2008 comparable to 2000 and 2004, just a slightly different amount of smoothing compared to Pollster's standard estimator this year. None of those differences change the qualitative picture or shift the magnitude of changes I cite above.

Trends in Party Identification in Wisconsin

This week my colleague Ken Goldstein and I conducted a Wisconsin statewide survey sponsored by the UW Department of Political Science and WisPolitics.com. So fair warning that I'm a party to this survey rather than an independent observer.

A number of people have commented on the party identification balance in the survey: 38% Dem, 24% Rep, 29% Independent (37% Independent when "no preference/other" are allocated to independent. When this group is asked how they "lean", very few insist on some other party, so this allocation makes sense.) See Alan Reifman's blog on weighting and party id for a good example and discussion of broader issues of weighting to party id.

I want to point out two things here and put our data in the context of other polls in Wisconsin.

The chart above shows party identification trends since 2000 using data from three sources that have done frequent polling in the state. What we see is a relatively stable Dem/Rep parity from 2000-2004, with Dem ID falling a bit around 2004 while Reps moved up slightly.

Starting in 2005, however, there is an initially slow but then sharper shift in partisanship. Republican ID declines from about 30% to about 24% today, while Dem ID rises from about 30% to nearly 40%. After an initial surge of independents, that group has recently fallen off a bit. (You have to squint a bit to see WPRI and Badger after 2005, but they are close to the trend lines during this period, so the changes are not just a matter of house effects or phone vs ivr methods. WPRI, for example, has Rep ID moving from 33% in 2004 to 28%, 26% and 25% in 2005-2007. Their Dem ID rises from 30%-33%-34% then falls to 29% over the same period. The final 29% is a large discrepancy from the trend, of course.)

We did not weight our survey to party identification, and these trends help explain why we have reservations about doing that. While relatively stable, party id does move over time, and by a fair bit, as you can see here. But that said, our unweighted results turn out to be quite close to the estimated trends in partisan categories in any case.

The second point is to compare these trends with those in exit poll measures of party id. In 2000, the VNS Exit poll put Wisconsin pid at 37% Dem, 32% Rep and 31% Ind. This shifted in 2004 to 35% Dem, 27% Ind and 38% Rep. But in 2006 the exit polls found that the balance was 38% Dem, 34% Rep and 27% Ind. Those values all show a smaller share of independents at the polls on election day compared to the polling trend, but that is to be expected given differences in turnout between partisans and independents. The size of the party ID groups grows as a result, but the balance between them is in line with what we see in the trends in the polls, though certainly not an exact match. The polls, after all, are of either adults or likely voters, while the exits are by definition a measure of who actually showed up on election day.

For 2006, the Dem exit percent and the Dem trend estimate are a close match. Republicans gain in the exits, by about 6 points over the 2006 trend estimate. If that holds for 2008, we might expect an electorate more like 38% Dem and 30% Rep. Of course both parties will have very active "ground games" and GOTV efforts to try to change those numbers.

While I'm certainly happy that our party id balance is so close to the trend in all the other polling, the more important point is that party id in Wisconsin has shifted quite a bit over the past four years. The coming campaign may alter that, possibly bringing disappointed former Republicans back home, for example. Likewise a Republican advantage in turnout could bring the exit polls back to closer balance. But as the data show, today the GOP is at the worst disadvantage the state has seen in over eight years.

Let me conclude with a bit of description of the polls used here.

Wisconsin Policy Research Institute ("WPRI") has done some of the longest running polls in the state, usually two a year. Their data here is taken from their annual estimates, which I assume pool the two surveys though they don't say so explicitly. WPRI describes itself as "Wisconsin's Free Market Think Tank".

The "Badger Poll" is conducted by the UW Survey Center. They did more extensive polling in 2002-04 but now do about two polls a year.

SurveyUSA is a well known national pollster that uses "Interactive Voice Response" (IVR) automated interviews. SurveyUSA has done monthly polling in the state since 2005, providing some of the best data on state trends in approval of elected officials and as a byproduct have an excellent data series of party ID.

Finally, there is our new Department of Political Science/WisPolitics poll. Ours uses a commercial call center, not the UW Survey Center or undergrads in a class calling for a grade. WPRI, Badger and our poll all use live interviewers, SurveyUSA uses IVR. Most of these surveys are in the 500-600 respondent range.

Gay Marriage Support and Opposition

Marriage for gay and lesbian couples has been a hot button issue, most especially so in the 2004 election cycle when 11 states considered and passed referendums banning (in various ways) same-sex marriages. In 2006 an additional 8 states voted on marriage ballot measures, with only Arizona defeating the proposal. In all, 41 states have statutes defining marriage as "between one man and one woman", and 27 states have put that definition into their constitutions. Only five states currently have no law banning same-sex unions (MA, NJ, NM, NY, RI). In 2008, Florida will have a "defense of marriage" amendment (DOMA) on the ballot, while California is awaiting certification of a ballot proposal and Arizona may reconsider its 2006 initiative (currently awaiting state Senate approval). (An excellent summary of the status of same-sex marriage in the states is available here.)

Despite this overwhelming majority among other states, the California Supreme Court last week ruled that the state cannot constitutionally withhold the right to marriage from same-sex couples. (Text of the ruling is here. The LA Times initial report on the decision is here.) Supporters of gay marriage hailed the decision as a breakthrough for fundamental rights, in line with the same California Court's decision in 1948 striking down laws banning inter-racial marriage. Opponents of gay marriage argued the ruling puts the issue squarely back on the table for 2008 and confirmed the opponents argument that only constitutional amendments can prevent courts from overturning popular opinion on this issue. In 2000 California passed, by a 61%-39% majority, Proposition 22 affirming that "only marriage between a man and a woman is valid and recognized in California."

California has one of the strongest domestic partnership laws in the nation, so the Court's decision has the effect of ruling that by withholding the designation "marriage", such domestic partnership laws still fall short of the equal treatment required by the state constitution.

The California decision follows the Massachusetts Supreme Court's ruling of November 18, 2003 which ultimately made Massachusetts the first, and so far only, state to legalize same-sex marriage. (Rhode Island law recognizes same-sex marriages from other states.) Subsequently, the state Supreme Courts of New York, New Jersey and Washington have each declined to find a constitutional right to same sex marriage. Four states have civil union laws providing full state-level spousal rights (CT, NJ, NH and VT) while six have domestic partnership laws that provide varying degrees of spousal rights (DC, HI, ME, OR, WA plus the California law at issue in this decision).

In light of the California decision, let's take a look at public opinion on same-sex marriage and how opinion has responded to past events.

A typical question asks "Do you strongly favor, favor, oppose, or strongly oppose allowing gays and lesbians to marry legally?" (This is the form used by the Pew Research Center polls. There is considerable variation in question wording, but most polling has used a similar dichotomy between favoring gay marriage or opposing it. I've collapsed "degrees" of support or opposition into a dichotomous measure for all polls.) The earliest use of such a question I could find dates back to September 1985, but it was not until 1992 that the question began to be asked regularly. There was a flurry of interest in the question following the Massachusetts ruling and during the 2004 election campaign.

If we rely on that first poll alone, in 1985 82% of the public opposed same sex marriage, while only 11% supported it. By the early 1990s, when the data become richer, opposition was at about 65% while support stood at about 28%. Congress passed, and President Clinton signed, the federal "Defense of Marriage Act" in September 1996, but public opinion trends seem not to have noticed at all, neither rising nor falling around that time. By the week of the California ruling, May 15, 2008, opposition had declined to about 55% while support had grown to 40%. The net effect of some 16 years of public debate was a 10 point decline in opposition and a 12 point rise in support.

But that trend was not uniform. The Massachusetts ruling, and the 2004 election campaign, coincided with a sharp, if relatively short term, disruption of the previous slow but steady decade long shift of opinion. The Massachusetts Court decision placed the issue squarely on the public radar, and the 11 state ballot proposals in the 2004 election created the setting for public debate and political exploitation of the issue.

During the year from November 2003 to November 2004, opposition to same-sex marriage rose by five points, from 55% to just over 60%. Meanwhile support fell by about eight points, from 38% to 30%, then rebounded by a point or so by election day. (These shifts slightly predate the Massachusetts decision, probably reflecting the increased visibility of the issue prior to the Court's ruling.) The impact of these shifts and of the 11 referendums that were passed on the presidential election remains debatable. Initial punditry credited the referenda with helping defeat John Kerry, especially in Ohio. More careful subsequent analysis doubts much of an effect, however.

These sharp shifts in trend reversed direction immediately following the 2004 election, but took more than two years to return to pre-2004 levels. Support returned to 2003 levels in mid-2007 while opposition has only now, in May 2008, declined back to where it stood in mid-2003. Despite this slow recovery from the 2004 "shock", the 2005-08 trend lines make it clear that public opinion returned to its previous trajectory of slowly rising support and declining opposition in the aftermath of 2004. It is also interesting that the 2006 elections, with 8 states voting on referenda, made no discernible difference to the post-2004 trend. In part this may reflect the more limited number of states, but it also reflects some decline in the saliency of the marriage issue.

The California ruling, and the likely campaign over a proposition there to modify the state constitution this fall, will test whether increasing the salience of the issue will result in a replay of the 2003-04 dynamics, with opponents stimulated and supporters in retreat, or if the 2006 experience means that the issue is no longer the motivator it was in 2004. The 2003-04 data clearly show the potential for sharp changes when the marriage issue becomes extremely salient. That the fight will take place in the most populous state in the Union also guarantees national exposure. However, the fact that most states have already settled this issue through law or amendment, and that only three states (so far) are on track to have proposals on the ballot, means that the issue is more localized than it was in 2004.

Opinion now is not much different from where it was in mid-2003, so a similar reaction is possible but there may be an element of "been there, done that" as well. The novelty of the issue is surely much reduced now than it was five years ago, though the record of referenda passing in 7 of 8 states in 2006 certainly demonstrates that opposition to same-sex marriage remained strong even in a very pro-Democratic election year. (Wisconsin, for example, reelected a Democratic governor and flipped a House seat to the Democrats but also modified its constitution to ban same sex marriage or anything substantially equivalent to marriage.)

The big question is whether the marriage issue has any carry over to the presidential vote in 2008. Democratic politicians, including Senators Clinton and Obama, have tried to insulate themselves by opposing gay marriage. Instead, they support civil union or domestic partner legislation. Senator McCain opposes same sex marriage and opposes legal recognition of same sex partnerships, but also opposes a federal constitutional amendment. This line of debate, with both parties opposing marriage, but with Democrats willing to support some legal recognition short of marriage, reflects another way to framing the question, one that is significantly more favorable for limited rights for gays and lesbians.


















(Note: This chart is scaled the same as the previous chart so the dynamics and time frame are directly comparable. The large white space prior to 2000 reflects the politically relevant point that in that time period the "civil union" option was not prominent enough to be included in polling questions.)

Beginning in 2004 (with one early exception in 2000), polling organizations began asking a question with three alternatives. The CBS News question wording is representative:

Which comes closest to your view? Gay couples should be allowed to legally marry, or gay couples should be allowed to form civil unions but not legally marry, or there should be no legal recognition of a gay couple's relationship?

When the "civil unions" option is added, opposition to gay rights drops significantly from about 55% to 40%. Likewise, support for gay marriage drops from 40% to 29%. The "comfortable" middle ground is then some 26% who are willing to support civil unions so long as they fall short of "marriage".

This "half a loaf" approach is acceptable to only some in the gay rights community, but it is precisely the politically acceptable position that Democratic politicians think can move them from the losing side of public opinion to the winning side. If we add supporters of marriage to supporters of civil unions, we get the chart below.


















This is now a near mirror image of the balance of opinion in the first chart. Now about 53% support either civil unions or marriage, and a minority of 40% oppose any legal rights for gay and lesbian couples. By assuming supporters of marriage will not punish them for the expedient support of only civil unions, Clinton and Obama (and many other Democrats) have tried to turn a losing position into a winning one.

The remaining uncertainty is whether opponents of any legal recognition are more intense than the supporters of civil unions. If so, then opposition groups may still win the battle between intense minority and lukewarm majority. On ballot propositions, the record is strongly in favor of the opponents of marriage and in some cases of civil unions as well.

The Clinton-Obama position will certainly not win over opponents of any form of legal recognition for gays, but then they probably wouldn't win many such voters in any case (an exception is African-Americans, many of whom are quite opposed to marriage or civil unions.) Whether their position provides them popular support in response to attack ads on this issue remains to be seen.

NC and IN Final Sensitivity Comparison

Both standard and sensitive estimators are agreed in North Carolina. In Indiana there is a little bit of room between them, but not enough to affect conclusions about the probable outcome (if the polls are right!)

The gyrations the Indiana sensitive estimator for Clinton goes through, thanks to variability in polls and relatively few polls, is a good warning that the sensitive estimator may just be a bit too ready to chase after noise.

NC and IN Final Pollster Comparisons

With the last of the preelection polls in, we can now do our "apples to apples" comparison. Follow each pollster in the charts to see who's high, who's low and who has jumped around.

Note this is for the Obama minus Clinton MARGIN (which makes it easier to plot all the polls in one, still jumbled, chart.)

And check back tonight as the votes roll in to see who nailed it and who missed. In North Carolina all agree on the winner, only the margin is in dispute. But Indiana has a little disagreement on who is ahead. Fun!

How much does the Pollster matter for Trend?

One of the things we think about a lot at Pollster.com is the quality of polling. Mark Blumenthal's post on the North Carolina poll demographics here is a great example of how much variability we see among polls, all trying to hit the same target population.

This issue is also raised by those who would like to exclude some polls from our trend estimates. If one "bad apple" spoils the barrel, then this is a serious issue for our efforts to estimate the state of the races here.

We've stuck to our principle that we include all available polls without cherry picking (to shift the fruit metaphor!) but we don't do that out of blind faith. Rather we do it because the empirical evidence shows that the effects of single pollsters are generally small, certainly compared to the other sources of uncertainty about the state of the race.

Here I take a look at this issue for North Carolina and Indiana.

There are four elements that affect how much a pollster influences our trend estimate.

First, the pollster's results must be "different" from the trend we'd estimate without them. If a pollster happened to hit our trend dead on every time, their influence would reinforce our trend estimate, but not change it. So for a poll to affect the trend, it needs to be different from what we'd otherwise estimate.

Second, the pollster needs to produce results that are systematically different from the trend. If a pollster bounces around the trend, some high and some low, then the net effect is small, even if individual polls are rather far off the trend.

Since the trend is determined across all pollsters, these first two points are another way of saying that the pollster must differ from what other pollsters are getting.

Third, volume matters. In some states, a single pollster accounts for a substantial proportion of all polling, while other pollsters contribute only a single poll. The former obviously have more potential influence than the latter. But high volume of polls doesn't matter if they are consistently close to (and scattered around) the trend estimate based on other polling. The problem comes when the prolific pollster is also rather different from others, and especially if there are few other pollsters active in the state.

Fourth, polls late in the game can have more leverage on the "current" trend estimate. So a pollster that does several polls but only in the last week before election day can have more influence on the current estimate than they would if those polls were spread over the entire pre-election period. Again, such an effect is only visible if the late polls are different from other polling.

Having an effect on the trend could be a very good thing if the pollster is right while others are wrong. The problem is how do you know a priori which pollster will be right THIS TIME. Experience this year demonstrates that a good day can be followed by a bad day, or both on the same day.

It is also important to put these effects in perspective across all polls we see in a race. The individual polls are highly variable. Our data often finds polls covering plus or minus 5, 6 or even 7 points of our estimated trend for an individual candidate, and double that for the margin between two candidates. There is a lot of noise out there, and the whole point of our trend estimator is to extract the signal from the noise. Our estimator (especially the "standard" estimator I'm using here, as opposed to the "sensitive" estimator we also check) is designed to resist polls that are "way off" (i.e. outliers) but at the same time be able to follow the common trend across polls. (I'm going to not go into the details of our local regression estimator here, which is not a simple rolling average. Let's hold that for another day. The FAQ on this is coming.)

So let's take a look at the North Carolina plot way up there at the top of this post. The horizontal axis is scaled to show the range of poll results we've seen in the state since April 1. This provides perspective on how much variation you see from poll to poll in the raw results.

The red "whiskers" at the bottom of the plot are the individual polls taken over this time. There is a bit more than a 25 point range in the Obama-Clinton margin during this period. Since the trends in the state have been relatively flat, only a little of this variation is due to "real change".

Our trend estimate based on all polls is the vertical blue line, which as of Monday afternoon is +8.6 points in Obama's favor.

How much do individual pollsters matter for this estimate? PPP has done the most polling in the state. If we take them out, the trend estimate drops to 7.0, a shift of 1.6 points on the difference (or an average of .8 points for each candidate, moving in opposite directions of course).

At the opposite extreme, removing Insider Advantage from our estimator produces a 10.7 point Obama lead, a shift of 2.1 points on the difference, or 1.05 points per candidate.

For most other pollsters, the effect is far smaller, even for relatively frequent pollsters such as SurveyUSA and ARG.

So the maximum effect of removing a single pollster is a shift between a 7.0 and a 10.7 point Obama lead. A shift of 3.7 points on the difference can matter in a close race, but that difference is relatively small compared to the variation we see in individual polls. Indeed, the four polls completed 5/4 show a range of +3 to +10 for the Obama margin. (They average a +7.25, compared to our trend estimate of +8.6.)

There is less polling in Indiana, so we might expect more influence since there are fewer polls to stabilize the trend estimator.


















Here the current estimate using all polls is -6.2, a lead for Clinton. The range of results we get from excluding pollsters is from -4.1 (excluding SurveyUSA) to -8.7 (excluding Zogby). That is a bit larger than North Carolina, as expected. But put this in the perspective of the range of raw poll results for Indiana, which is from -16 to +5 in polls taken since April 1. The six latest polls as of Monday, all ending on 5/4, range from -12 to +2.


To sum up. Which polls we include affect our results. That both has to be and should be. We WANT the data to matter, and of course it does. What we don't want is for individual polls to make such large differences for our results that inclusion or exclusion decisions become critical. The results we see here show that we SHOULD be somewhat uncertain as to the trend, as it depends upon which individual pollsters are included. What is somewhat different in our approach at Pollster.com is we want to emphasize this uncertainty and put it in perspective, rather than produce a single number and treat that as if it were "certain". That is why we always show the individual polls spread around our trend estimate in the charts. All estimates have uncertainty. We need to understand both the value of the estimate and the uncertainty inherent in it. Pollster effects are part of that story.

However, what is crucial is that these effects on the trend estimate are small compared to the range of variability we see across individual polls. The goal of our trend estimator is to produce a better estimate than what any single poll (or pollster) can provide. By that standard pollster effects on the trend are modest compared to the variability across individual polls.

Evaluating the accuracy of the polls is a different topic, one we'll revisit again on Wednesday.

NC and IN Sensitivity Update

As we close in on tomorrow's primaries in North Carolina and Indiana, the "standard" and "sensitive" trend estimates have largely converged.

In North Carolina the standard estimator puts Obama at 50.1% and Clinton at 41.5%. The sensitive estimator has it Obama 49.5% and Clinton 42.2%. Or, a margin in the standard trend of +8.6 for Obama vs +7.3 in the sensitive estimate.


















In Indiana, the standard estimator puts Clinton up 49.5% to 43.3% for Obama. Switching to the sensitive estimator makes it Clinton 51.2% to Obama's 43.5%. Or a Clinton advantage of 6.2% for the standard estimator versus 7.7% for the sensitive one.

Either way the polls are seeing a split decision tomorrow. Anything else will be a very interesting surprise.

Final Pennsylvania Updates

Clinton has increased her lead in the trend estimates over the course of the last polls to 6.6 points using the standard estimator, and to 8.4 points using the sensitive estimate. Last minute polls have given her bigger margins.

Now the key question is whether undecideds push her over a 10 point win, or whether increases in turnout by new "unlikely" voters raises Obama's total.


















Still a good bit of variation and some pollsters see a strong trend, others not so much.


















Pollster variation doesn't make a lot of difference in our trend estimates.

But remember, since the polls don't allocate undecided, both they and the trend estimates are leaving some 8 percent of voters on the table. They will go somewhere, and if they break disproportionately for Clinton you have a "huge win", while if they go overwhelmingly for Obama you have a nail biter or a dramatic come-from-behind win. In previous primaries, the "winner" has usually enjoyed a significant increase in support beyond what the last polls showed.

Pennsylvania Undecided Voters

Senator Clinton currently holds a 6 point lead over Senator Obama in Pennsylvania, based on our Pollster Trend Estimate, 49%-43%. But that leaves about 8 percent undecided. What they do will determine whether Clinton's vote expands her lead compared to the polls, or if the undecided narrow or possibly reverse, the lead.

My partner at Pollster, Mark Blumenthal, has looked at this using aggregate polling data here and in his NationalJournal.com column here.

In this post I take a look at the individual level, though using data that are three weeks old, so use caution in extrapolating to tomorrow's electorate.

Using data from the Time/SRBI poll of Pennsylvania, conducted 4/2-6/08, I estimate a model of support for Obama compared to Clinton. I use "the usual suspects" as variables predicting vote: partisanship, gender, race, Hispanic ethnicity, region of the state, age, education, religion and income. The data at that time found an eight point Clinton lead, a bit higher than today's trend estimate.

Using the coefficients for "decided" voters, I can estimate the probable vote of the undecided 11% of voters in the poll. This gives us a look at how they would be expected to behave IF they behave like those who have already picked a candidate. (Note the "if" here. As with all models, this assumes stable influence of the variables among the undecided as among the decided.)

The plot above shows the distribution of estimated probability of voting for Obama. Values close to zero are very likely to support Clinton, while values close to 1 are very likely Obama supporters. Those close to .5 are flipping a coin. The shape of the distribution gives a sense of where voters "lump up" in their estimated preferences.

The black line plots the distribution among those who reported a vote preference. The red line plots the distribution of estimated support among those who said they were undecided in early April.

The key point is that the undecided resemble the decided, with a small shift to the left, suggesting they were as a group somewhat more likely to support Clinton. In these data, the primary difference between undecided and decided voters was age, with older voters more likely to say they hadn't decided. As we've seen in virtually every exit poll, older voters are more likely to support Clinton, so the result we find here, that the undecided lean a bit more towards Clinton, is consistent with this result.

Now again for the caveats. These data are three weeks old. The model requires the assumption that undecided voters ultimately behave like those who decided. Different variables as predictors can make a difference. And so on.

The goal here is NOT, NOT, NOT a prediction of tomorrow's vote. Much may have changed since the first week of April.

The point is to illustrate what we can learn about undecided voters beyond the simple fact they say "undecided". In this case, the data suggest they are not wildly different from those who decided, but their older age makes it more likely they ultimately lean more to Clinton.

The Time/SRBI data are archived at the Roper Center for Public Opinion Research. I am solely responsible for the analysis here.

Pennsylvania Pollster Comparison

Judge for yourself.

Day Before Pennsylvania Sensitivity Update

The Pennsylvania race has turned slightly toward Clinton over the weekend, with her lead now at an even 6 points in our standard trend estimate. If you believe in taking more chances with random noise, the sensitive estimator has a 6.4 point Clinton lead.

In the rush of new polling over the weekend, it is also good to check how much any of them may be affecting our estimates.


















Dropping any single pollster makes only a bit of different to our estimates. The Clinton trend ranges from 48.5% to 49.6%, while Obama ranges from 42.6% to 43.5%. So dropping your least favorite pollster can, at most, account for the difference in a 5 point race and a 7 point one.

And note that we still have about 9 percent undecided. I wonder what they will do?

National Dem Trends, Newsweek Poll

A new Newsweek poll gives Barack Obama a 54%-35% lead over Hillary Clinton among Democratic voters (story here, detailed results here, and thanks to Newsweek and their pollster, Princeton Survey Research Associates International, for a full and complete disclosure of the details of their survey. A model others should be encouraged to follow.)

The Newsweek poll raised a few eyebrows for its 19 point Obama lead, considerably more than other recent polls, and beyond the 10.4 point Obama lead in our trend estimator. However, a closer look at recent data shows that Newsweek is not far from other recent data. Newsweek is the 6th poll in April with Obama at or above 50%, while five April polls put him below 50%. With Clinton, Newsweek is the 4th April poll putting her at or below 40%, while eight polls have her above 40%. So Newsweek shows a larger Obama lead than others, but it is not as far out of line as may first appear. (Note in the counts of polls above, we only count independent samples of the Gallup daily tracker, so dont' count each of their daily results as new polls.)

As you can see from the plots below, we've not seen many recent outliers in the national Democratic nomination polling, and the new Newsweek is well within the 95% confidence interval.






















All that said, our trend estimate for the race puts Obama at 50.2% and Clinton at 39.8%, a significant gain for Obama during the month of April. Since late March, Clinton has suffered a somewhat greater downward slope while Obama's gains have been a bit more shallow, implying a slight gain among undecided voters.

The Newsweek poll also has some interesting internal results. As with virtually all this year's polling, Obama has a substantial lead among Independents who will vote in the Democratic primary or who lean Democratic: 61% to 28% for Clinton. What is a key to Obama's strength in the Newsweek poll is he ALSO leads among self-declared Democrats 51% to 38%, a group Clinton has won in most contests. If real (and I want to see more data before I accept this change) then Obama may be winning the consensus among party rank and file that will be key to persuading Superdelegates to move strongly in his direction. So long as he trails among the strongest party identifiers, that case is less persuasive. Pennsylvania provides a new test of this possible change in support. (Obama continues to trail in our Pennsylvania estimates, so it is unlikely he has so far persuaded a majority of Democratic identifiers there, though stay tuned for Tuesday's exit polls.)

The other important shifts in this national Newsweek poll is that Obama leads among men 57%-31% but also among women 52%-38%. Again this would represent an important gain among women.

The age gradient in Obama support has been interesting all year. In the Newsweek poll, he wins 18-39 year olds by 62%-28%, as usual, but also wins 40-59 year olds by 54-36%. In past exit polls, his "break even point" has varied among age groups from as low as 40 (i.e. losing all groups over 40 years old) to as high as 59 (only losing those over 60 years old.). More astonishing here is he gains a plurality of those over 60, 47%-41%, which if true would be his best performance among older voters all year.

The area of the Newsweek poll where Obama still suffers is among working class or poor whites, where he trails badly, 35%-54%. In contrast he leads 52%-35% among upper and middle class whites. That class divide remains a critical issue for his campaign.

A caution here as well. In any poll with such high overall support, the support almost has to reach across many subgroups (not quite as a mathematical certainty, but as a strong empirical regularity.) So we should be careful not to accept the depth of Obama's support among Democrats, women and those over 40 years old until we have more evidence from additional polling. In the exit polls this year, where we see big Obama wins (VA, MD, WI) we also saw him making strong inroads among these groups. But with the margin he achieved in these states, it would have been hard NOT to have done well across groups. Be careful of the cause and effect attributions here. It is a challenging state like Pennsylvania that can reveal how deeply into the various demographic groups Obama has managed to extend his appeal. But with those cautions, Newsweek's poll shows some evidence that the national Democratic constituency is moving in his direction across a number of groups.

If these changes are real, we'll see new polling that reflects it. If just a favorable poll (though not an outlier!) then new polling will show that these groups are not quite as enthusiastic for Obama as the current poll suggested.

Pollster Effects on Pennsylvania Trends

There is a lot of interest in the differences among pollsters, and especially what effect they have on the perception of the race. Here at Pollster, the interest is specifically on the question of whether individual pollsters drive our results, and if so by how much.

So here is a quick look at those effects in Pennsylvania's Democratic primary.

The chart above shows the trend estimates that result from dropping each pollster in turn, and reestimating the trend without that pollster. This is a specific test of how much it matters whether we include a particular pollster or not.

Over the 15 pollsters we have represented in Pennsylvania, the estimates excluding each one for Clinton range from 46.6% to 48.3. The estimate with all pollsters included is 47.4% for Clinton.

For Obama, the estimates range from 41.2% to 42.5%, with the estimate for all pollsters at 42.0%.

The upshot is that pollsters do matter, but none drive the results by very much. A 1.7% range on Clinton and a 1.3% range on Obama for the trend estimate is very small compared to the range we see across the raw poll results. Another example of the greater stability of the trend estimators we use compared to the substantial variability across polls.

We can look at the effects of each pollster by comparing the trend estimate without that pollster to the estimate with them. The higher the effect, the more that pollster drives our trend estimate up for that candidate. Negative effects means the pollster drives our estimate down. Again, this is compared to the trend with and without the individual pollster.

The two charts below show these effects for Clinton and for Obama.


















For Clinton, SurveyUSA has the highest positive impact on our trend estimate, followed by Rasmussen. At the opposite end, PPP has the largest negative effect on our trend, with Zogby/Newsmax the next largest negative effect. Other pollsters are clustered rather closely around zero.

And it is important to note that even the four largest positive and negative effects are all less that 1 percentage point.


















For Obama's trend, Quinnipiac shows the largest positive effect, followed by Zogby and PPP with near identical effects. On the negative end, SurveyUSA has the most negative effect of Obama trend. Again, none of these effects is as much as one percentage point, and SurveyUSA's is less that half a percentage point. Other pollsters have less impact.

We can also look at the joint effects. These are the same as seen individually above but plotted against one another.


















Pollsters do matter, and outliers matter even more. But the net effect of any individual pollster on our trend estimates in Pennsylvania are modest, especially when viewed in comparison to the wide range of raw poll results for each candidate. Another advantage of combining information across polls rather than pick single polls we "like".

Pennsylvania Dem Sensitivity Comparison

Here is an update on the Pennsylvania Trend Estimates for both the standard estimator and the more sensitive one.

The difference is small: 0.3 for Clinton and 0.8 for Obama. But hey, it can be a game of inches. Either way it looks like about a 5 point margin right now.

(See earlier posts for details on the standard and sensitive estimate. The sensitive is about twice as responsive to the data, but tends to chase ghosts.)

Pennsylvania Dem Trend Sensitivity

Time for a look at the sensitivity of our trend estimators. ARG has a new Pennsylvania poll out showing a 20 point Clinton lead. But Susquehanna Polling has one completed three days earlier with a 3 point Clinton lead and Zogby has one on the same day with a 4 point Clinton lead. Did things shift that swiftly or do we have an outlier?

Our standard trend estimator is designed to resist outliers, and it manages to do so in this case (see the chart above.) With or without ARG (and with or without ARG AND the close Susquehanna poll) the trend estimates only change by 10ths of a percentage point. What does change slightly is the slope of the trend estimate between the solid line with all polls and the dashed and dotted lines without ARG and without ARG and Susquehanna. In fact, the changes are slight enough you need to squint to really see them.

It may surprise you that removing ARG makes Clinton's trend estimate go UP, when you would understandably expect it to go down. The reason is simply that she is trending down either with or without ARG. Removing ARG means that the latest poll for the trend estimate is 3 days earlier, hence higher up on the downward trend. Since ARG doesn't much affect the slope, removing it just "backs the trend up" by three days, making Clinton a tiny bit better off. The same happens in reverse for Obama-- without ARG he is a shade worse off (0.1 percentage points) because his trend is rising either way, so backing up 3 days hurts him a tiny bit. (Removing ARG and the close Susquehanna poll makes similarly modest changes to the trend estimate.)

So for our standard estimator, whether we include or exclude the latest ARG poll makes very little difference.

That is by design. At this point a single new poll that shows a big change should be regarded with caution. It MAY reflect a big shift over the weekend. But it could just as easily be a statistical fluke that will not be replicated in other new polls. Until there is more evidence one way or the other, the trend estimate is designed to not chase after a single poll far away from the other data. But if we get two or three more polls showing similar results, the trend estimator will then be convinced the shift is real, and will turn in the direction of the new data.

But what if we decided to be less cautious and more willing to respond to new polling? For that, we have an alternative estimator that is about twice as sensitive. This one will pick up new trends much more quickly, but will also be misled by a single outlier much more easily. Let's see what this more sensitive estimator thinks is going on.

















With the sensitive estimator, the ARG poll makes a HUGE difference. It shifts the difference in trends from a 4.3 point Clinton lead to a 12.6 point lead! That is really responsive. But it also demonstrates what a large difference a single poll can make when we crank up the sensitivity of the trend estimator.

What is more interesting with the sensitive estimator is that taking out ARG, we see a flattening of Obama's trend and even a tiny downturn, though also a continued decline for Clinton. If we also take out Susquehanna we find Obama continuing to rise but Clinton falling at a slower pace than without ARG alone. (You really have to squint to see the dotted line. Sorry about that.) Clinton leads by 4.2 without ARG AND without Susquehanna, by 4.3 without ARG alone.

So perhaps the sensitive estimator is showing us something new-- Obama may have flattened or even turned down a shade recently, but if so Clinton seems to have continued to decline as well. This also illustrates why we prefer our more conservative estimator. The sensitive version is just too dependent on individual polls at the end of the series. It provides a possible early hint of things to come, but is too unstable to count on. Our standard estimator may be a little slow to pick up a change of direction, but it seldom chases after random noise.

As for ARG's result, let's wait a day or two and see what other polls have to tell us and how our estimator responds.

For an animation of the Pennsylvania sensitivity analysis for a wide range of sensitivity, download this Acrobat file and use the arrow keys to control the animation speed.

Bush Approval Falls to 28.3%

President Bush's approval trend has taken a sharp downturn in recent weeks, to fall to a new low for the administration at 28.3%. This follows a lengthy period of stable approval at around 32-33%.

Recent polls from Gallup and AP/Ipsos put approval at 28%, a new low for the Gallup poll. Harris recently found approval at 26% while CBS News put approval at 28%. Pew similarly has approval at 28%, though the Diageo/Hotline result for registered voters (as opposed to adults in the other polls) has approval at 35%, the only recent poll over 30%.

While the President has taken a back seat to the primaries in recent months, his new approval slump reflects growing pessimism over the economy which has displaced the war in Iraq as the most important problem facing the country. Likewise the percent saying the nation is headed in the wrong direction has continued to grow in recent months, to a high of 81% in a recent CBS News poll.

Most Important Problem, 2005-2008

The Iraq war and the economy have consistently been the top two "most important problems" facing the nation during President Bush's second term. But the dynamics have changed dramatically over the past seven months.

After near parity in 2005, the war dominated throughout 2006 as far more important that the economy, and with rising numbers of people citing the war as most important. That peaked in early 2007 with concern over the war gradually diminishing through most of the rest of the year.

And then the economy struck. As recently as August 2007 only 8% said the economy was the most important problem. By early September that jumped to 13%, then to 23% in January and now 37% in early April. By contrast the war fell from 34% to 15% over that same time.

It will be ironic if the fall campaigns largely ignore the war to focus on an economy that 12 months earlier had looked fairly good.

California Super Tuesday Pollster Comparison

There is quite a bit of disagreement in the California polls, so let's do a Pollster Comparison to see who says what.

The Democratic race has the biggest gap across pollsters. Most see Clinton ahead, but disagree on how much the race has tightened. But Suffolk and Rasmussen put Obama just barely ahead in their final polls. And the big difference is in the Zogby/Reuters/C-SPAN poll that sees Obama not only ahead but expanding his lead to double digits.

That gives us a range of results from Obama ahead by more than 10 to Clinton ahead by 10. Somebody is not quite right here. But who? And why?

Across all the polls, Clinton is relatively flat while Obama has gained. But looking at each poll and each candidate reveals more differences across pollsters.

Both Zogby and the Field poll find some decline for Clinton while others have her flat or rising (SurveyUSA and Rasmussen).






















Everyone sees Obama either flat or rising, with no pollster (who has at least 2 polls) seeng Obama declining. But the extent of the rise, and how high Obama's starting point was, differs quite a bit across pollsters. Survey USA and Rasmussen both see Obama gains, but SurveyUSA offsets that by measuring gains for Clinton as well, resulting in relatively little net change over their last three polls. Rasmussen, on the other hand, has Clinton gains but even bigger Obama gains, resulting in a net decline and a final poll with Obama just barely ahead.






















The Zogby polls in contrast find both Clinton declines AND Obama gains, making for a net change that strongly favors Obama and results in his 13 point lead in the final Zogby poll for California.

On the Republican side, we also see substantial differences. Two pollsters see a dramatic tightening of the race. Rasmussen and SurveyUSA estimate that McCain's earlier lead has now collapsed to a dead heat. (A single ARG poll also sees a dead heat, but has no over time data for comparison of trend.) In contrast the LA Times/CNN/Politico and Field polls both find McCain gaining some ground in their polls. These two are a bit stale now, but showed gains even when Rasmussen and SurveyUSA saw declines, so this is not only a difference of survey dates.

Zogby/Reuters/CSPAN is again quite different, finding Romney leading in all three polls and expanding his lead to high single-digits in the last two polls.























Across the Republican polls, the differences are almost all matters of the degree of increase for both McCain and Romney. All polls agree that McCain has been increasing his support. But they also agree that Romney is rising sharply. The differences in net support have a lot to do with differing estimates of how fast and how far Romney has risen. Those with the greatest Romney rises have him catching McCain or leading him.

Given the length of time it is likely to take to count the California vote, it may be Thursday before we know which of these polls was closer to the end result.

Super Tuesday Endgame

Updated: 2/5/08 at 1:59 pm est


















Now that the first "Super" event of the week is over, time to turn to the next one.

We've got a number of polls in several states, fewer polls in others. Here are the trends in the 17 states for which we have polls since January 1.

In the Republican chart below, I've omitted Utah where Romney holds an 84-4 lead over McCain, according to the one Republican poll since January 1. Expanding the scale to include that data point makes it hard to see the differences in all the other states.

See the individual state charts at Pollster.com for trend estimates in the states with sufficient polling. Here, look at the data and reach your own conclusions. The data here are through Sunday. I'll update the charts Monday evening with the Monday polls.

Super Tuesday Polling at a Glance

Updated: 2/5/08, 1:58pm est













































No time for commentary this morning, so here is an explanation.

It is ironic and annoying that the most important date on the primary schedule is also the date with the fewest polls per state. Just as the campaigns are struggling to run 22 simultaneous campaigns, so pollsters and the media have invested little in comprehensive polling of the Super Tuesday states. Even large states such as New York and California have fewer than 10 polls since January 1, far fewer than we saw last week in Florida for example. As a result, we have many states with no data at all, preventing a comprehensive overview of the prospects for Tuesday. Even where we do have polls, we lack enough to consistently estimate the trend with data taken since Iowa. Where we can estimate trends, we've done so on the "regular" state pages at Pollster.com. You should go there for the best trend estimates we can manage with so little data.

The charts here are a way of seeing the entire set of Super Tuesday states (where we have polling) at a glance.

Rather than plot the usual trends with so few data points, each poll is a point and the darker the point the more recent the poll. The points are also scaled in size to be proportional to the number of delegates at stake in the state.

Instead of a trend estimate, this plot highlights the median of all post-Iowa polling in the state. The shading of points will then let your eye tell you whether there is a visible trend around that median. Be your own data analyst!

When more states become available, they'll be added to updated charts. If a state is missing, we don't have polling for it. (If you think we've missed a state with polling data, let us know!)