ch 12 sample surveys

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Sample SurveysChapter 12



Purpose of Data Analysis 1. Collect data

2. Summarize data

3. Draw conclusions about a larger group



Main Ideas! Examine a part of the Whole

Randomize!

It¶s the Sample Size that matters



How big of a ³spoon´ or

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

or population?



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



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



StatisticNumber that is computed from the

sample data

Mean standard deviation

ss

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

x



Cautions about Sample Design Poor design

Convenience sample

Voluntary response

Bias

Sample design that systematically favors certain

outcomes



Voluntary Response People choose themselves by responding

to a general appeal

Give an example



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



Ways to Choose an SRS Draw names from a hat

Use computer software or calculator

random number generator Random number digit table



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



How to Choose an SRS 1. Label

2. Table



ACTIVITY Random Rectangles



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



Cautions about Sample Surveys Undercoverage

Nonresponse

Response Bias

Wording effects

Video #18 Sample Surveys



ACTIVITY Rolling Down the River

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



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



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.

ch 12 sample surveys

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