The RAND presidential poll is an interesting one because it polls the same group of people week after week. Each participant is polled once a week, and the total is averaged over the week. There are two important limitations to this methodology that need to be borne in mind:
- The original sample has sampling error, like all polls, but that error is propagated throughout the poll, whereas if fresh samples are drawn, it will cancel out over time. For this reason it is misleading to consider the absolute margin as a good indicator of the state of the race - the same non-representativeness of the original sample will be present in every total. However, what this means is that its usefulness lies in the direction of the trends, which will tend to be far less noisy than when a new sample is drawn each day, whilst the opposite is true of conventional polls (sampling error cancels out over time, but makes the trends noisy).
- Polling people regularly will itself tend to focus their minds to the race - as a result, by now, this is probably a group of people that have shown an atypical degree of interest in the race. However, it occurs to me that in that sense it may mimic the opinions of those in swing states who have been much more heavily targetted with news, conventional polls, and ads. So perhaps RAND may be regarded as a kind of proxy measure of attitudes in swing states.
So what I did was to plot the RAND margin, relative to its own baseline, i.e. with the margin artificially set to zero (in fact the Pollster model has Obama 1.4 points ahead on that date, which is what the RAND poll originally showed, so this is conservative), and simply tag a few key events.
Romney got a small bounce from his VP announcement, and from the RNC convention.
He took a major hit from the release of the 47% video, from which he was recovering around the time of the first debate.
Obama got a big bounce from the DNC convention, and caught the 47% video wave just as the DNC wave was subsiding. After the first two presidential debates, Obama got a very temporary (immediate response of people polled the day after?) upswing, followed by a decline, although Biden's debate was followed by a steadier rise for Obama (possibly because the hit Obama took from the first debate was subsiding anyway). Then, since the final debate, Obama's margin has risen to almost peak levels.
So, if RAND can be regarded as a measure of how people well-tuned to the race have reacted to key events, I'm really hopeful. The message I'm taking home is that among attentive voters:
- Obama's margin has a net rise since July
- His gains have exceeded his setbacks
- He has gained since the final debate
- These trends may be a good proxy for voters in swing states
Onwards and upwards!