Final 2004 Presidential Election Gallup PollRhajiv Ratnatunga

STATS 1000 Seminar 21

Polls are used by politicians and their supporters to gauge their likely election day performance.

Gallup Statistical Model

“President Bush held a 49-47 edge over Sen. John Kerry when the undecided voters were not allocated to a particular candidate. When Gallup, using a statistical model that assumes that 9 of 10 of those voters would support Kerry, allocated the voters, the poll ended as a dead heat with each candidate garnering 49%.”

What does this mean?

This was the estimate

95% Confidence Interval for Unknown Population Proportion

Estimate +/- margin of error

= sample proportion +/- 2 standard deviations

almost = to sample proportion +/- 2 standard errors

= p hat +/- 2 sqrt ((p hat (1-p hat))/n)

Explain the multiplierThe standard error

Since the population proportion is unknown…..

The test for normal approximation is revised by….

Replacing the population proportion with the sample proportion

np becomes np(hat)

and

n(1-p) becomes n(1-p(hat))

Since n is big, we can say without doing calculations that both tests will be larger than 10

Kerry/ Edwards

Bush/ Cheney

Nader/ Camejo

Other (vol.)

None (vol.)

No opini

on

Likely Voters            

2004 Oct 29-31 ^† 47 49 * 1 * 3

Final Allocated Estimate

49 49 1 1 -- --

“Results based on likely voters are based on the subsample of 1,573 survey respondents deemed most likely to vote in the November 2004 General Election, according to a series of questions measuring current voting intentions and past voting behavior. For results based on the total sample of likely voters, one can say with 95% confidence that the margin of sampling error is ±3 percentage points.”

.47 + 2 *sqroot ((.47(1-.47))/1573) = .495 = 50%

John Kerry -

.47 - 2 *sqroot ((.47(1-.47))/1573) = .444 = 44%

(44%,50%) = Confidence interval for Kerry

.49 + 2 *sqroot ((.49(1-.49))/1573) = .515 = 52%

George Bush

.49 - 2 *sqroot ((.49(1-.49))/1573) = .444 = .46%

(46%, 52%) = Confidence interval for Kerry

The margin of error given was accurate.