Ch 12 Sample Surveys

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 1/21

Sample SurveysChapter 12

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 2/21

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 3/21

Purpose of Data Analysis 1. Collect data

2. Summarize data

3. Draw conclusions about a larger group

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 4/21

Main Ideas! Examine a part of the Whole

Randomize!

It¶s the Sample Size that matters

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 5/21

How big of a ³spoon´ or 

sample size do you need toget a ³taste´ of the ³soup´

or population?

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 6/21

Designing Samples Population [parameter]

Entire group of individuals we want infor mation

about Sample [statistic]

Part of the population we actually examine to

gather the infor mation

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 7/21

Parameter 

Number that describes the population

Mean Standard deviation

In practice, the value of a parameter is not

known«we use sample statistics toestimate it

 Q

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 8/21

StatisticNumber that is computed from the

sample data

Mean standard deviation

ss

In practice, we often use a statisticto estimate an unknown parameter 

 x

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 9/21

Cautions about Sample Design Poor design

Convenience sample

Voluntary response

Bias

Sample design that systematically favors certain

outcomes

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 10/21

Voluntary Response People choose themselves by responding

to a general appeal

Give an example

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 11/21

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 12/21

Simple Random Samples SRS

Consists of n individuals from the

population Chosen in such a way that every set of n

individuals has an equal chance to be the

sample actually selected

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 13/21

Ways to Choose an SRS Draw names from a hat

Use computer software or calculator 

random number generator  Random number digit table

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 14/21

Random Number Digit Table Each entry is equally likely to be any of the

10 digits from 0-9

Entries are INDEPENDENT of each other 

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 15/21

How to Choose an SRS 1. Label

2. Table

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 16/21

ACTIVITY Random Rectangles

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 17/21

Probability Sampling Designs Each member of a population has the same

chance of being selected

Examples: 1. SRS

2. Stratified Random Sample

3. Mu

ltistage sam

ple 4. Systematic

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 18/21

Cautions about Sample Surveys Undercoverage

Nonresponse

Response Bias

Wording effects

Video #18 Sample Surveys

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 19/21

ACTIVITY Rolling Down the River 

http://www.coopext.colostate.edu/TR A/ Agronomy/SweetC/scseedtreat3.jpg

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 20/21

What Could GoWrong? Lot¶s of stuff!

See pages 236 ± 240 and add comments

to your notes NO  AMOUNT OF NUMBER CRUNCHING

can fix B ADLY collected data

8/8/2019 Ch 12 Sample Surveys

http://slidepdf.com/reader/full/ch-12-sample-surveys 21/21

SUR V

EY

 P

ROJECT

Create a separate Survey document

[The questions should be clear and concise. There should be a placefor students to

indicate their response]

Discu

ss the W¶s of you

r investigation [Who, What, When, Where, Why,HOW]

Describe the population for your study

Describe the Sample and how you will select your sample [remember thata convenience sample or an Internet survey are basically worthless for f urther inference]

What is the sampling frame that you chose?

DO NOT CONDUCT the survey. Using a REPORT FORM AT present theinfor mation in written for m.

See Mrs. Shyrock if you have any questions.