Monday, August 11, 2008

Nothing is happening in the presidential campaign

The best couple paragraphs I've read about political polling in a while:
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. Beyond that, doing one poll per day throughout a long campaign would mean that you’d expect to see one or two relatively rare outlier results per month even under circumstances of total stasis. And as Alan Abramowitz points out if you look at the daily results this is actually what you see — incredible volatility with Obama’s lead oscillating violently around an average of 3-4 points. Since it’s not plausible that the public mood is really swinging anywhere near as rapidly as a very naive reading of the Gallup daily results would suggest, people could see that this is basically statistical noise in a stable race.

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. But while I have no way of proving that it’s just statistical noise and nothing’s really happening, the “nothing happening” narrative is completely consistent with the data, and it’s telling that the conventional narratives collapse when the data is presented in different ways whereas the “noise” narrative is consistent with multiple ways of displaying the information.

Emphasis added. I'm in favor of the null hypothesis here: Obama has a 3-4 point national lead. He's had it for a while. And not much is happening. There's a tiny sliver of the population that's sighing and gasping with every new ad, response, gaffe, and poll. And I am a member of this sliver, certainly. But that doesn't mean that millions of American voters are changing their mind every couple days.


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