On August 1 when I had my last day at The Atlantic it was time for panic as McCain had tied things up. Then Obama started to regain ground, going up to a four point lead. Then the race tightened again, then Obama opened up a five point lead, and now it’s tightening again but with Obama back to a smallish lead having beaten back the strong challenge McCain was mounting around August 1. In short, McCain’s “Celebrity” ad and drilling attacks were working well, but when the McCain campaign went after Obama on the tire gauge thing he came up with effective countermeasures and regained his lead.
Or maybe none of that happened. As everyone knows, there’s sampling error associated with polling. As a result, if you poll 1,000 people on August 1 and then you poll 1,000 different people on August 2 you shouldn’t be surprised to see the results differ by several percentage points even in the absence of any change in the underlying public opinion....
But Gallup doesn’t report its daily results, they report a multi-day rolling average. Abramowitz notes that if you report a ten day rolling average, you get a chart where nothing happens — Obama maintains a flat lead of 3-4 points. Again, a stable race. But if instead of doing either of those things you do what Gallup actually does and report a three day rolling average, you get these pleasant looking peaks and valleys in the race. The change over time here is large enough in magnitude (unlike on the ten day chart) but also slow enough in pace (unlike on the one day chart) to be plausibly interpreted as public opinion shifting in response to events. And since the human mind is designed to recognize patterns and construct narratives, and since it suits the interests of campaign journalists to write narratives, people interpret the peaks and valleys of the three day average as real shifts in public opinion.
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