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.
Top Related