1. Pre-Algebra Mrs. Spanier
Sampling
Pre-Algebra
Mrs. Spanier

2. Questioning
Should be fair
No answer should appear better than another
This is called bias

3. What is “Population”?
The community (zip code, age, gender, etc…) of people whose opinions are sought.
Usually so large and diverse that it is impossible to ask each member of the group every question.
Why we select a sample.

4. Random Sample
Members of the population are chosen in a way that all have an equal chance to be measured.
Also called representative and proportionate sampling because all groups should be proportionately represented.

5. Stratified Sample
Strata means to spread out.
Population is divided into two or more strata (classes or groups) and each is sampled randomly.

6. Every nth member of the population is sampled.
Systematic Sample
Every nth member of the population is sampled.

7. What kind of sample?
George went through the telephone book and called every 89th person listed.
Systematic
5 students from each home room are questioned.
Stratified

8. What kind of sample?
Four people divided the telephone book evenly and each randomly sampled from their portion.
Stratified

9. What kind of sample?
A computer selects families all over the U.S. to receive a survey in the mail.
Random

10. What kind of sample?
Every 20th person to exit the Gap is questioned about their purchases.
Systematic

11. The End

12. Happy Tuesday! 2 biased questions 1 fair question Tell your neighbor…
About the 3 types of sampling methods
2 biased questions
1 fair question
Day 2 of activity

13. Let’s Share… Find another pair from a different group. Discuss #1-6:
Do your numbers agree?
Are these answers valid? Why or why not?

14. Let’s Share… Discuss #7… Is each a valid sample? Too big, too small?
World number is around 100 million and mostly women and children. Why do you think this is?
Day 3 wrap up
World Statistics