Section 1.3
Summer 2013 - Math 1040
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Roadmap
Data collection.
Experimental design.
Sampling techniques.
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Simple random sample
A simple random sample, or SRS, is a sample in which each possible
sample of the same size has the same chance of being selected.
Selection of an SRS can be done in at least two ways:
Random table of digits.
Random number generator.
Both methods required the population subjects to be ordered and labeled.
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Example - Sleep Deprivation
18 people volunteer for a study on the effect of sleep deprivation on motor
skills. 9 will be chosen as a control.
01
04
07
10
13
16
Jake Busey
Lucy Liu
Bridget Fonda
Susan Boyle
Dan Regan
Judy Greer
02
05
08
11
14
17
Mariah Carrey
Ron Perlman
Carlos Mencia
Vanessa Hudgens
Kate Upton
Mary Poppins
03
06
09
12
15
18
Mike Judge
Adam Baldwin
Steve Martin
Rick Ross
Pete Townsend
Connie Chung
We will use a table of random digits and a random number generate to
select a sample for the control.
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Table of Digits
A table of random digits is found in the book’s Appendix B, page A7.
Here is the first line:
92630 78240 19267 95457 53487 23894 37708 79862 76471 66418
Broken into pairs:
92 63 07 82 40 19 26 79 54 57 53 48 72 38 94 37 70 87 98 62
76 47 16 64 18
We select the first nine instances of the numbers 01 to 18, without
replacement for our control group.
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Sampling Techniques
There are four additional types of sampling techniques that are frequently
used:
Stratified Samples
Cluster Samples
Systematic Samples
Convenience Samples
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Sampling Techniques
Stratified samples divide the population into sepearte groups, then
selects an SRS from each group.
In a study regarding student opinion on stem cell research, the surveyor
divides the student population with respect to majors and randomly selects
students to question from each major.
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Sampling Techniques
Stratified samples divide the population into sepearte groups, then
selects an SRS from each group.
In a study regarding student opinion on stem cell research, the surveyor
divides the student population with respect to majors and randomly selects
students to question from each major.
Cluster samples takes an SRS of clusters (such as city blocks) and uses
all subjects in those clusters.
Five classrooms are selected at random from all classrooms and each
student in those classes are questioned.
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Sampling Techniques
Systematic samples, every possible subject is numbered (at random) and
every regular interval of subjects are sampled.
In quality inspection, every sixth product is checked for defects.
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Sampling Techniques
Systematic samples, every possible subject is numbered (at random) and
every regular interval of subjects are sampled.
In quality inspection, every sixth product is checked for defects.
Convenience samples consist of available members of the populations. It
is not recommended.
As students leave the library, they are asked to fill out a survey of their
study habits. 1
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Assignments
Assignment:
1
Recommended exercises.
2
Go to http://www3.norc.org/GSS+Website/ the GSS homepage.
Take some time to get used to searching it.
Vocabulary: Simple random sample, stratified, cluster, systematic,
convenience.
Understand: Strengths and weaknesses of different kinds of sample
techniques.
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