1. Quiz
20 minutes

2. Day 5: Margin of Error
Unit 1: Statistics

3. Today’s Objectives
Students will define, explore and calculate Margin of Error

4. Estimating Population Parameters
Vocabulary for this lesson is important!
Parameter a value that represents a population
Statistic a value based on a sample and used to estimate a parameter

5. The Basic Paradigm Sample Population Inference Parameter Statistic
Margin Of
Error
µ - mean
σ – standard deviation
x̄ - mean
s – standard deviation

6. Margin of Error – page 11
Suppose that 900 American teens were surveyed about their favorite ski category of the 2002 Winter Olympics in Park City, Utah. Ski jumping was the favorite of 20% of those surveyed. This result can be used to predict how many of ALL 31 million American teens favor ski jumping.
Read first paragrah

7. Margin of Error – page 11
To determine how accurtely the results of surveying 900 American teens truly reflect the results of ALL American teens, a margin of error should be given.
When pollsters report the margin of error for their surveys, they are stating their confidence mathematically in the data they have collected.

8. Calculating the Margin of Error
Margin of error is a “cushion” around a statistic
ME =
This formula only works with answers that are 5% or more of the sample size
n = sample size

9. For our Winter Olympics example, the margin of error would be , or 3%
Since the actual statistic could be larger or smaller than the true amount, the margin of error can be expressed as ± 3%
We can confidently state that the true proportion of American teens who favor ski jumping falls between 17% and 23%.

10. Margin of Error – page 11
Work in your groups to answer questions 1-8 on page 11. Time Keeper: 10 minutes Reader/Recorder: Read each question out loud

11. Margin of Error – page 11
Find the margin of error for a survey of 100 American teens.
Compare the margin of error to the margin of error of 900
Find the margin of error for a survey of 9,000 teens
90,000 teens
± 10%
A survey with only 100 teens had a larger margin of error
± 1.1%
± .3%

12. Margin of Error – page 11
Draw a conclusion about the margin of error based on the size of the sample.
If you want to cut your margin of error in half, what would you have to do to the sample size?
What if you wanted your margin of error to be 5%? How large would your sample need to be?
Find the sample size needed to create MOE of 2%
The larger the sample size, the smaller the MOE
Your sample would have to be 22 bigger or 4x bigger
2500

13. Homework
Complete the worksheet about Margin of Error on page 12