1. 5.1 Sampling and Producing Data

2. Our survey question:

3. Vocabulary observational study—does not attempt to influence response
experiment—imposes some treatment on individuals
population—entire group of individuals
sample—part of the population we actually examine

4. Vocabulary sampling—asking a part of a population
census—attempts to contact every individual

5. Example
Observational study or an experiment? Who is in the population? How are we going to sample?

6. Sampling Designs
Voluntary Response—people choose themselves to respond
Call-in poll, online poll, etc
Example:

7. Sampling Designs
Convenience—choosing individuals who are easy to reach
Mall surveys, asking your friends at lunch
Example:

8. Sampling Designs
Simple Random Sample (SRS)—every individual has an equal chance of being chosen. Also, every “group” has an equal chance of being chosen.
Drawing from a hat, table B, calculator

9. Sampling Designs Steps for a SRS:
Label every individual in the population with a number.
State when you should stop sampling. (how many do you want?)
Use Table B (or your calculator) to select numbers at random.
List who is in your sample.

10. Practice: pg. 341 #9
You must choose an SRS of 10 of the 440 retail outlets in New York that sell your company’s products. How would you label this population? Use Table B, starting at line 105 to choose your sample.

11. Practice pg. 341 #10
Choose 3 resorts, using Table B, starting on line 131

12. Sampling Designs
Stratified Random—divide population into groups; do an SRS within each group
Use a characteristic to divide that may be important to your data (Example: gender, race, geographic location, age groups)
Example:

13. Sampling Designs
Cluster Sampling— population is already divided into groups (clusters)
Clusters are chosen randomly; then ALL individuals are chosen to answer
Example:

14. Practice pg. 342 #13
A poll of opinion in CA uses random digit dialing to choose telephone numbers at random. Numbers are selected separately within each CA area code. The size of the sample in each area code is proportional to the population living there.
A.) What is the name for this kind of sampling method?

15. B.) Here are the area codes in CA: A different method would be to choose 10 area codes using a SRS using Table B starting at line 111.

16. Homework: pg. 333 #1, 2, 4, 7, 8
1.) Population: All local businesses. Sample: the 73 businesses that return the questionnaire, or the 150 businesses selected. Nonresponse rate= 51.3% 2.) A. An individual is a person; the population is all adult US residents for that week. B. An individual is a household; the population is all US households in the year 2000 C. An individual is a voltage regulator; the population is all the regulators in the last shipment

17. 4.) We can never know how much the change in attitudes was due to the explanatory variable (reading propaganda) and how much to the historical events of that time. 7.) Only persons with a strong opinion on the subject will respond to this advertisement. 8.) Letters to legislators are an example of a voluntary response sample- the proportion of letters opposed to the insurance should not be assumed to be a fair representation of the attitudes of the constituents.

18. HW: pg 333 #1, 2, 4, 7,8