Tuesday, August 07, 2007

Clinton vs. Obama: Dueling Memos and Some Data

The Clinton and Obama campaigns released dueling memos yesterday, each touting their standing in some polls and dismissing evidence to the contrary. The Clinton memo is here and the Obama memo here thanks to our friends at MSNBC. Both memos, not surprisingly, selectively interpret the polls to their advantage. But let's look at the data and see who has the better evidence at this point.

The national polls have shown a long period of stability. Obama enjoyed a nice rise in the polls after he became a candidate following the 2006 election. He had a rapid rise to 23% by April 1 and it was nearly impossible to read a news article about him during this period without encountering the phrase "rock star". But perhaps he was a "one-hit-wonder" because since April 1 there has been no further upward movement in his national support. If anything there has been a negligible decline to a current estimated support of 22.6%. That has put him solidly in second place since November, but he has failed to close the gap with Clinton since April.

The Clinton campaign also experienced a long period in the doldrums. After entering 2006 at about 37% support, Clinton declined slightly to 35% just after the November elections. And there she sat until May. There were hints of tiny increases and tiny declines, but she remained well within a point of 35% during the spring. This stability could be interpreted as evidence of strength because her support was sustained throughout the period of Obama's rise. I think this reflects the power of Clinton's hold on her core supporters. At the same time, during this period of ramping up of the campaign there was no detectable improvement in Clinton's standing with Democratic primary voters.

That began to change by early June and has accelerated a bit since. My best estimate of Clinton's current support is 38.8%, a rise of nearly 4 points since the end of April. That four point rise won't sound like much to those accustomed to the noisy variation from poll to poll, but the trend estimator I use has the advantage of aggregating across many polls and hence has a much smaller range of random variability. A move of this much is certainly not negligible.

The blue line in the figure is my standard trend estimator. The red line is more sensitive to short term trends, but also more easily fooled by random noise. I provide both so you can judge for yourself any differences between the more solid blue estimator and the more rapid change of the red estimate. In this case, the red estimator is in complete agreement with the blue for Obama, but suggests a slightly greater surge for Clinton recently.

Of the 90 national polls included in my data, Clinton has led Obama in 89. But the more important point is that gap has not closed since April 1, and since May the gap has widened a bit with Clinton's move up and Obama's stagnant polling.

The Obama memo characterizes the " irrelevant and wildly inconsistent national polls" as meaningless. As the figure above makes clear, there is indeed considerable variation across national polls, but the story they tell is not inconsistent except when cherry picking results. The polling varies in about the random pattern around the trend that we would expect from surveys based on probability samples of the electorate.

On the other hand, the Obama memo is quite correct that nomination races are about performance in individual states, not national polls. The early primaries have carried great weight in the modern period since the reform of the primary system in 1972. There is great debate this year about whether this will continue or if the massive February 5th primary day will fundamentally alter the traditional dynamics. But everyone agrees that it is better to do well in the pre-February 5 primaries than to do badly in them. So let's see where the Democratic campaign stands in the first five caucus and primary states.

The available state polling substantially agrees with the national polling in putting Clinton ahead of Obama in all five of the first states, based on my trend estimate that incorporates all polls. Moreover, Clinton's support is stable or rising in all five states, while Obama has risen substantially in only South Carolina, and perhaps a bit in New Hampshire. In Iowa Obama's support has clearly fallen off, while Nevada and Florida appear essentially flat.

The important caveat here is that state polling is more limited than national, and that the numerous polling organizations vary in their results with some sometimes substantial "house effects". Either campaign can (and both do) select individual polls in the states to make the case for their improving standing. But this is pure cherry picking of data. With the variability clear in the plot, it is easy enough to pick the poll that puts your candidate at the highest mark while finding one that minimizes your opponent's standing. That is the reason we use all the data here and let the trend estimates fall where they may.

So where does this leave the race? A clear Clinton advantage and strong evidence of some recent improvement in both national and state polls. For Obama, there is no comparable upturn nationwide and the picture in the states is mixed at best. The Clinton upturn is of interest because some argued that her support was solid but had little or no upside. "Everyone" has already decided about Clinton, this line of argument goes, and so while her base is rock solid she is vulnerable to a coalition of "anybody but Clinton" voters. That vulnerability remains a real liability, but the recent upturn suggests the upside for her is not as limited as some analysis suggested.

The bright side for Obama is that he still has a considerable upside in public awareness and in favorability, an area where Clinton does indeed seem in some peril among the general electorate. Obama also has very impressive fundraising success which indicates support among more engaged partisans.

The critical question is what happens to the roughly 60% of Democratic voters who currently do not support Clinton. Can they be won over or can Obama (or someone else) become the focus of an "anybody but Clinton" coalition? Until that dynamic is sorted out, and until some candidate other than Clinton starts to move up (none, so far) the advantage has to go to Clinton.