Understanding Margin of Error in Polls

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Questions and Answers

What is the typical margin of error for the difference between two candidates compared to that for an individual candidate?

Half that of the margin for an individual candidate
Three times that of the margin for an individual candidate
About the same as that for an individual candidate
Twice that of the margin for an individual candidate (correct)

How much should the Republican candidate be ahead for us to be confident their lead is not due to sampling error?

At least 10 percentage points
At least 8 percentage points
At least 4 percentage points
At least 6 percentage points (correct)

What is the meaning of a margin of error of plus or minus 8 percentage points for a 3-point shift between two polls?

The difference indicates a reliable change in support levels
The actual shift could be anywhere from a 5-point decline to an 11-point increase (correct)
There is a definite increase of 8 points in the Republican’s position
The sampling methods were inconsistent across the polls

What condition must be met for a shift in polling numbers to indicate a real change in the race?

The observed change needs to be large enough to be above statistical noise (C) Signup and view all the answers

In Poll A, with a 3-point margin of error, what is the expected range for the Republican's true position relative to the Democrat given a 5-point lead?

Between -1 and +11 percentage points (B) Signup and view all the answers

What is the general interpretation of a 8-point margin of error for the difference in two polls?

It reflects high levels of sampling variability (A) Signup and view all the answers

Why is it cautioned to interpret large swings in polling support at face value?

They may not be statistically consistent with actual voter behavior (D) Signup and view all the answers

What does an increase in the Republican lead from Poll A to Poll B indicate if both polls have the same margin of error?

The observed increase may still fall within sampling variability (B) Signup and view all the answers

What does a margin of error of plus or minus 3 percentage points at the 95% confidence level indicate?

We expect the result to be within 3 percentage points of the true population value in 95 out of 100 surveys. (B) Signup and view all the answers

Which statement best describes what it means for a candidate's lead to be 'outside the margin of error'?

The candidate is leading by an amount greater than the margin of error. (A) Signup and view all the answers

How does sampling error impact the reported support for individual candidates?

It shows that individual support varies and has an associated margin of error. (D) Signup and view all the answers

What additional step must be taken to determine if a race is 'too close to call'?

Calculate a new margin of error for the difference between the two candidates’ support levels. (B) Signup and view all the answers

Why might reporting on horse-race poll results be more complicated than it appears?

Statistical principles are often misapplied or misunderstood. (C) Signup and view all the answers

What does the margin of sampling error enable us to understand about a survey result?

It indicates how close a survey result is likely to be to the actual population value. (C) Signup and view all the answers

What range of support does a candidate with 48% and a margin of error of plus or minus 3% potentially fall into?

Between 45% and 51% (A) Signup and view all the answers

What is the significance of being a 'smart consumer' of survey data?

Evaluating polls critically and understanding statistical nuances like margins of error. (D) Signup and view all the answers

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Study Notes

Margin of Error in Polls

The margin of error is a measure of the precision of a poll's results.
It represents the range within which the true population value is likely to lie 95% of the time.
A margin of error of +/- 3 percentage points means that if the same poll is conducted 100 times, 95 times the result will be within 3 percentage points of the true value.

Determining Leads

A candidate's lead is "outside the margin of error" if it is greater than what sampling error would account for.
To determine if two candidates are tied, calculate the margin of error for the difference between their support levels, which is usually about twice as large as the margin for each individual candidate.
A lead of 6 percentage points with a 3-point margin of error for each candidate is considered a "statistical tie."
A lead of 8 percentage points with a 3-point margin of error is considered significant and unlikely to be due to sampling error.

Measuring Change

The margin of error for the difference between two polls can be larger than expected.
A change in support between two polls may not indicate a real shift if it is within the margin of error for the difference.
To confidently detect a change between polls, the observed difference needs to be large enough to be statistically significant.
While large swings in support may occur, it is important to be cautious in accepting them at face value.

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