First let me explain the methodoloy used. The different combinations of VP candidates produced very large ranges of potential support. For instance, in Virginia, this ranged from Obama winning by 18 with Edwards as his running mate against McCain/Pawlenty, to losing by 6 points with Sebelius as his running mate against McCain/Lieberma, a swing of 24 points:
In addition to these topline results, SUSA released cross-tabs, allowing us to analyze the swing among Democrats and Independents as well. So we will use these swings as pretty good proxies for the amount of voters in play in each of these categories-at least at this time-and see what they tell us.
We beging with a somewhat busy chart, that has the advantage of making it clear how we're proceeding-we will simplify the picture, once I've explained where things are coming from. The chart has two heavy lines, showing how the two candidates did in each state, in head-head competition with no VPs, and four lighter lines showing their highest and lowest totals of all the VP matchups listed. It's organized in ascending order of Obama's head-to-head vote:
Now, for our purposes, we're not really interested in the straight-up head-to-head results, so we just drop those lines out and get a simpler picture:
Next, we simplify further by shifting from ranges of votes to the swing between the high and low end of the ranges. This reduces each state from four data points to two. But then we add a new data point-the average of the two swings. That's because the swings are not symmetrical, due to people who don't choose either candidate. This new data point is actually half of the total swing, since the total swing is the sum of the swings for both parties. But taking the average leaves everything on a similar scale, so that's the figure I've chosen to use:
This chart is the simplest overall summary of just how many voters are in play, percentage-wise, in each of the states.
Now it's time to take a similar look at the independents and Democrats. But since we've been through this whole process once, we don't really need to do it again. We can go striaght to the final graph, that has the most information in the simplest-to-grasp form.
Indepedents and Democrats Compared
Independents clearly have a very wide degree of variation in support (swing), as we would normally expect. Indeed, the variation itself varies considerably from a low of just under 10% to a high of over 50% (remember the chart shows the average swing of the two candidates, we have to double it to get the total swing.)
In contrast, the Democrats show generally lower levels of swing, and less variation in these levels, from about 18% to about 28%:
However, as Chris noted, Democratic party membership is up. And SUSA provides voter registration figures that allow us to weight the totals from the above charts. We can then take the weighted figures and combine them with figures for all voters for each state, and come up with the following chart, that clearly shows the vartiation in Democratic support dominates over the variation among independents:
Finally, here is the data from the last chart, in table form, with the addition of columns that show how large the Democratic and independent swings are as a percentage of the over-all swing:
|Swing Range Based on VPs|
|  ||Amount of Swing||Percent of Swing*|
|* Swings are not strictly additive, as they represent maximums from a range of values, but can safely be directly compared.|
Thus, we see that on average, the Democratic swing of 10.8% is almost half of the total swing, and is 4.4% higher than the independent swing of 6.4%. That is truly a much more important group of voters, numerically. But, of course, another way to look at it is that Democrats are, as usually, a cantankerous lot, and there's a lot of room to go to bring them all together. The good news, however, is that now that they are a much larger group than the Republicans, or the independents, there's a much bigger payoff for bringning them together.
[Update]: It seems pertinent to note that the Rasmussen Daily Tracking Poll has Obama with 80% of the Democratic vote against McCain for the first time since the polling began:
The Rasmussen Reports daily Presidential Tracking Poll for Saturday shows Barack Obama attracting 46% of the vote while John McCain earns 42%. When "leaners" are included, Obama now leads 48% to 45%. Leaners are survey respondents who initially do not favor either candidate but indicate their support on a follow-up question. One week ago today, McCain had the edge over Obama, 46% to 43%....
Obama's bounce is primarily the result of Democrats beginning to unify behind his candidacy. For the first time all year, Obama is supported by 80% of Democrats over McCain. In recent months, his support from Democrats has typically been in the high-60's or low-70's range.
I hope the analysis above gives you a greater sense of satisfaction in hearing this news.