Science Behind The News: Opinion Polls & Random Sampling

MALE NEWS PRESENTER 1: A major winter storm [OVERLAPPING]

MALE NEWS PRESENTER 2: The bruising fight [NOISE] to win Tuesday's Republican [OVERLAPPING]

MALE NEWS PRESENTER 3: Most dangerous virus. [NOISE]

MR GINGRICH: With your help, we're going to win a historic victory.

FEMALE NEWS PRESENTER: The 2012 presidential campaign is in full swing,

with Republican candidates battling state by state to

determine who will face President Barack Obama on election day.

MALE NEWS PRESENTER 4: In the poll numbers we are debuting tonight,

there is a new GOP front-runner in this race.

FEMALE NEWS PRESENTER: A crucial part of this grueling electoral process is polls,

the almost daily snapshots of public opinion,

that help measure who's up and who's down among the candidates. [MUSIC]

PRESIDENTIAL CANDIDATE: Thank you.

DR VINCENT HUTCHINGS: The aim of an opinion poll is to get a sense about a population and where they [NOISE]

stand on some particular set of issues or policies to measure their attitudes and effect.

FEMALE NEWS PRESENTER: [MUSIC] Vincent Hutchings,

an NSF-funded professor of political science at the University of Michigan,

says that public opinion polls rely on a concept in statistics known as random sampling.

The idea that it is possible to draw a clear picture about

the feelings of a large group of people by examining how a small,

randomly assembled slice of that group feels.

DR VINCENT HUTCHINGS: The process involves interviewing a very small subset of that population

and doing so in a scientific manner so that you'll have a better accurate sense

but more efficient sense,

of what the entire population understands.

FEMALE NEWS PRESENTER: An opinion poll might focus on a particular state,

such as Florida, or the entire US population of more than 300 million people.

Pollsters use computer programs to generate a random list of

a few hundred or a few thousand telephone numbers from the larger group.

Then they call each number to survey people for their opinions.

Hutchings says making a random sample is a lot like cooking soup.

You don't need to eat the whole pot to know if it tastes good,

you just need a spoonful.

DR VINCENT HUTCHINGS: The cook merely needs to get a spoon out, taste it.

That spoon represents a sample,

as it were, of the actual contents of the pot.

FEMALE NEWS PRESENTER: [MUSIC] Samples, in general, give better poll results when they include

more characteristics of the whole population

and in the same proportions as the population.

Back to the soup analogy,

if you're cooking chicken soup,

you want your sample to include the ingredients such as chicken,

noodles, and broth in the same proportions as the overall soup.

DR VINCENT HUTCHINGS: We want to make sure that the sample has

the population characteristics that are

demonstrated in the larger population to which we want to make an inference.

FEMALE NEWS PRESENTER: When reading a poll, it's important to also study the fine print,

usually at the bottom.

You'll find information there about how the poll was

conducted and what the size of the random sample was.

You'll also find the margin of error,

a number with a plus or minus sign in front of it.

This number tells you the range of accuracy of the poll.

In this case, 3-5% points.

Typically, the smaller the margin of error,

the more accurate the poll is.

DR VINCENT HUTCHINGS: What that means is that the number that's reported in that survey,

we have a sense that given the size of the sample,

and given the level of uncertainty associated with that size,

the number could be 3-5% points higher or lower.

But we know it's in that range.

FEMALE NEWS PRESENTER: [MUSIC] Even though the polls rely on

just a slice of the population to gauge public opinion,

they are far more accurate than you might think.

[NOISE] Which is one reason why they play such a special role in politics.

DR VINCENT HUTCHINGS: Public opinion polls provide us with a way

absent an actual election to discern where the public stands on various issues.

FEMALE NEWS PRESENTER: As election day 2012 draws closer,

the science of public opinion polls will help give

a clear snapshot of who might be our next president.