Margin of Error

Recap…

Give three examples of each…

POPULATION SAMPLE1. 1.

2. 2.

3. 3.

What is a Margin of Error (MOE)?

• A value that tells the uncertainty in our estimate.

• A measure of how close we believe the SAMPLE proportion is to the POPULATION proportion.

• Formula used to predict MOE with 95% confidence ≈ 1 √n• The margin of error is roughly two standard deviations away

from the mean.

Example #1

During the week of 8/10/01, CNN conducted a poll asking 1000 Americans whether they approve of President Bush’s performance as President. The approval rating was 57%. In their next poll conducted during the week of 9/21/01, CNN conducted the same poll asking 100 Americans whether they approve of President Bush’s performance as President. The approval rating was 90%.

Answer the following questions…

1. Why the difference in ratings?

2. Find the MOE in the August poll.

3. Find the MOE in the September poll.

4. Explain why the MOE for the August poll in less than that in September.

Example #2

• Read the following article: http://usconservatives.about.com/od/campaignselections/a/Polls-And-The-Margin-Of-Wrongness.htm

Answer the following questions…

1. Why is it that MOE plays an extremely valuable part in what we refer to as “swing states?”

2. Name 3 “swing states” predicted for the 2016 election.