11/15/2007 04:41 pm ET Updated May 25, 2011

Mellman on What Poll Responses Mean

We have been talking quite a bit lately about the difficulty
pollsters have in identifying "likely caucus goers" in Iowa. Pollsters face similar challenges in
any similarly low turnout primary (a phenomenon that is more common than you
think) as well as in general elections (though not to the same degree). The
underlying problem for all pre-election polls is the same: When you ask people if
they are "likely" to vote in a future election, they tend to be far too
optimistic in their predictions. That is especially true if the pollster makes
it easy to say yes, by including "somewhat likely" as an answer category.

For different reasons, the candidate that voters prefer "if
the election were held today," is often different from the candidate they
actually choose on Election Day.

In a must-read
in The Hill, Democratic
pollster Mark Mellman helps us understand why:

For 25 years, I've counseled clients and colleagues
to consider psychological research demonstrating that people are very poor
reporters of their own decision-making processes. It reveals that we have
little reason to believe much of what people tell us directly in focus groups
and polls about why they do what they do.

Though it is heresy for a pollster to say it, the
evidence also suggests people are only mediocre predictors of their own
behavior. Responses to horserace questions a year out may be a special case of
faulty prediction.

Mellman also cites a paper by political
scientists Gary King and Andrew Gelman titled, "Why Are American Presidential
Election Campaign Polls So Variable When Voters Are So Predictable?" Over at
the Horse Race Blog, Jay Cost unpacks
the findings of the King-Gellman paper which focus on polling in general
elections. He offers this quick synopsis:

Gelman and King offer what they call the
"Enlightened Preference" Model. They assert that:

(1) Voters do not have full information throughout the campaign about
the "fundamental variables" that ultimately drive vote choices.

(2) Voters do use all available information to make their decisions.

(3) Voters do not rationally account for uncertainty during the course of
the campaign.

This explains how polls can vary so wildly, and yet
final results can be so predictable. Voters base their election decisions on
basic variables. Thus, their vote choices are quite predictable. But it is only
at the end of the campaign that they have fully grasped the values of the
variables. Additionally, they do not factor this lack of knowledge into their
thought processes. And so, when pollsters dial them up - they rely on the data
they have available, but give answers that are less certain than they realize.

Both Mellman and Cost go into more detail. Both posts are well worth the click.