Yglesias Yglesias guest-blogger Alyssa Rosenberg flagged this really interesting London Review of Books essay. Here's my favorite excerpt:
Yet if the voting patterns have been so predictable, why have the
polls been so volatile? One of the amazing things about the business of
American politics is that its polling industry is so primitive. Each
primary has been preceded by a few wildly varying polls, some picking
up big movement for Clinton, some for Obama, each able to feed the
narrative of a contest that could swing decisively at any moment. All
of these polls come with warnings about their margins of error (usually
+/–4 per cent), but often they have been so far outside their own
margins as to make the phrase ridiculous. A day before the California
primary in February, the Zogby organisation had Obama ahead by 6 per
cent – he ended up losing by 9 per cent. In Ohio, the same firm put
Obama ahead by 2 per cent just before the actual vote – this time he
lost by 10 per cent. The sampling of national opinion is even worse.
Before the Indiana primary, two national polls released at the same
time claimed to track the fallout from the appearance of Obama’s former
pastor Jeremiah Wright on the political stage. One, for the New York Times, had Obama up by 14 per cent, and enabled the Times to run a story saying that the candidate had been undamaged. The other, for USA Today, had Clinton up by 7 per cent, leading the paper to conclude that Obama was paying a heavy price.
The
reason for the differences is not hard to find. American polling
organisations tend to rely on relatively small samples (certainly
judged by British standards) for their results, often somewhere between
500 and 700 likely voters, compared to the more usual 1000-2000-plus
for British national polls. The recent New York Times poll
that gave Obama a 12 per cent lead was based on interviews with just
283 people. For a country the size of the United States, this is the
equivalent to stopping a few people at random in the street, or
throwing darts at a board. Given that American political life is
generally so cut-throat, you might think there was room for a polling
organisation that sought a competitive advantage by using the sort of
sample sizes that produce relatively accurate results. Why on earth
does anyone pay for this rubbish?
The answer is that in an
election like this one, the polls aren’t there to tell the real story;
they are there to support the various different stories that the
commentators want to tell. The market is not for the hard truth,
because the hard truth this time round is that most people are voting
with the predictability of prodded animals. What the news organisations
and blogs and roving pundits want are polls that suggest the voters are
thinking hard about this election, arguing about it, making up their
minds, talking it through, because that’s what all the commentators
like to think they are doing themselves. This endless raft of educated
opinion needs to be kept afloat on some data indicating that it matters
what informed people say about politics, because it helps the voters to
decide which way to jump. If you keep the polling sample sizes small
enough, you can create the impression of a public willing to be moved
by what other people are saying. That’s why the comment industry pays
for this rubbish.
Update: See commenter AlanSP below for some significant caveats about this take on polls.
--Michael Crowley