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Sampling Design and Procedu
Lecture & Seminar
If you decide whether or not you want to see a
new movie or television program on the basis of
the coming attractions or television
commercial previews, are you using a sampling
technique? A scientific sampling technique?
Population
Sampl
e
Sampl
e
Sampl
e
Sampling Terminology
Why Sample?
Pragmatic Reasons
Accurate and Reliable Results
Destruction of Test Units
www.mktginc.com
Stages in the Selection of a Sample
165
bee-dsm.in
Practical Sampling Concepts
Practical Sampling Concepts
Defining the Target Population
 What is the relevant population?
 Whom do we want to talk to?
 Population is operationally defined by specific
and explicit tangible characteristics.
The Sampling Frame
 A list of elements from which a sample
may be drawn; also called working
population.
 Sampling Frame Error
 Occurs when certain sample elements are not
listed or are not accurately represented in a
sampling frame.
168
Sampling Units
Sampling Unit
A single element or group of elements subject to
selection in the sample.
1. Primary Sampling Unit (PSU)
2. Secondary Sampling Unit
3. Tertiary Sampling Unit
169
Random Sampling and Non-sampling
Errors
Random Sampling Error
 The difference between the sample result and
the result of a census conducted using
identical procedures.
 A statistical fluctuation that occurs because of
chance variations in the elements selected for
a sample.
Non-Sampling (Systematic Sampling) Error
 Systematic (nonsampling) error results from
nonsampling factors, primarily the nature of a
studys design and the correctness of
execution.
1610
 Less than Perfectly Representative
Samples
 Random sampling errors and systematic
errors associated with the sampling
process may combine to yield a sample
that is less than perfectly representative
of the population.
Random Sampling and Nonsampling
Errors (contd)
Errors Associated with Sampling
1611
http://bee-dsm.in/Tools_1.aspx
Sampling Technique
1613
Probability Sampling
A sampling technique in which every
member of the population has a known,
nonzero probability of selection.
Nonprobability Sampling
 A sampling technique in which units of
the sample are selected on the basis of
personal judgment or convenience.
 The probability of any particular member
of the population being chosen is
unknown.
Probability versus Nonprobability
Sampling
1614
Nonprobability Sampling
http://lc.gcumedia.com/hlt362v/the-visual-learner/convenience-sampling.html
Nonprobability Sampling: Convenience Sampling
Obtaining those people or units that are most conveniently available
www.memrise.com
Nonprobability Sampling: Judgment (Purposive) Sampling
An experienced individual selects the sample based on personal
judgment about some appropriate characteristic of the sample member.
Nonprobability Sampling: Quota Sampling
Ensures that various subgroups of a population will be represented
on pertinent characteristics to the exact extent that the investigator
desires.
BUYERS RESPONDENT QUOTA
(SAMPLE SIZE= 200)
MEN 40% 80
WOMEN 60% 120
Nonprobability Sampling: Snowball Sampling
A sampling procedure in which initial respondents are selected by probability
methods and additional respondents are obtained from information provided by
the initial respondents.
slides.com
1619
Probability Sampling
 Simple Random Sampling
 Assures each element in the population of an
equal chance of being included in the sample.
 Systematic Sampling
 A starting point is selected by a random process
and then every nth number on the list is
selected.
 Stratified Sampling
 Simple random subsamples that are more or less
equal on some characteristic are drawn from
within each stratum of the population.
www.nedarc.org
Probability Sampling: Simple Random Sampling
Assures each element in the population of an equal chance
of being included in the sample
Probability Sampling : Systematic Sampling
A starting point is selected by a random process and then
every nth number on the list is selected
http://lc.gcumedia.com/hlt362v/the-visual-learner/systematic-sample.html
Probability Sampling: Stratified Sampling
Simple random subsamples that are more or less equal on
some characteristic are drawn from within each stratum of
the population
http://lc.gcumedia.com/hlt362v/the-visual-learner/stratified-sample.html
1623
 Proportional Stratified Sample
 The number of sampling units
drawn from each stratum is in
proportion to the population size of
that stratum.
 Disproportional Stratified Sample
 The sample size for each stratum is
allocated according to analytical
considerations.
Proportional versus
Disproportional Sampling
Disproportional Sampling: Hypothetical
1624
1625
Probability Sampling: Cluster Sampling
An economically efficient sampling technique in which the primary
sampling unit is not the individual element in the population but a large
cluster of elements. Clusters are selected randomly.
http://lc.gcumedia.com/hlt362v/the-visual-learner/cluster-sampling.html
1626
Multistage Area Sampling
Involves using a combination of two or more
probability sampling techniques.
 Typically, geographic areas are randomly selected
in progressively smaller (lower-population) units.
 Researchers may take as many steps as necessary
to achieve a representative sample.
 Progressively smaller geographic areas are chosen
until a single housing unit is selected for
interviewing.
http://bee-dsm.in/Tools_1.aspx
Sampling Technique
1628
What is the Appropriate Sample
Design?
Degree of accuracy
Resources
Time
Advanced knowledge of the
population
National versus local project
1629
Internet Sampling is Unique
 Website Visitors
 Internet surveys use unrestricted
samples.
 May not be representative.
 Panel Samples
 Recruited Ad Hoc Samples
Determination of Sample
Size
Frequency Distribution of Deposits
1731
Percentage Distribution of Deposits
1732
Probability Distribution of Deposits
1733
1734
Factors of Concern in Choosing
Sample Size
1. Variance (or Heterogeneity)
 A heterogeneous population has more
variance (a larger standard deviation) which
will require a larger sample.
 A homogeneous population has less variance
(a smaller standard deviation) which permits a
smaller sample.
2. Magnitude of Error (Confidence Interval)
 How precise must the estimate be?
3. Confidence Level
 How much error will be tolerated?
1735
 Sequential Sampling
 Conducting a pilot study to estimate the population parameters so
that another, larger sample of the appropriate sample size may be
drawn.
 Estimating sample size:
Estimating Sample Size for Questions
Involving Means
1736
Sample Size Example
Suppose a survey researcher, studying expenditures
on lipstick, wishes to have a 95 percent confident
level (Z) and a range of error (E) of less than $2.00.
The estimate of the standard deviation is $29.00.
What is the calculated sample size?
1737
Sample Size Example
Suppose, in the same example as the one before, the
range of error (E) is acceptable at $4.00. Sample size is
reduced.
Calculating Sample Size at the 99
Percent Confidence Level
17-38
Determining Sample Size for
Proportions
17-39
Determining Sample Size for
Proportions (contd)
17-40
753
=
001225
.
922
.
=
001225
)
24
)(.
8416
.
3
(
=
)
035
( .
)
4
)(.
6
(.
)
96
1.
(
n
4
.
q
6
.
p
2
2
=
=
=
Calculating Example Sample
Size at the 95 Percent
Confidence Level
17-41
Low Dispersion versus High
Dispersion
1742
LOs
1. Explain reasons for taking a sample rather than a
complete census
2. Describe the process of identifying a target
population and selecting a sampling frame
3. Compare random sampling and systematic
(nonsampling) errors
4. Identify the types of nonprobability sampling,
including their advantages and disadvantages
5. Discuss how to choose an appropriate sample
design
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10409004.ppt

  • 1. viewords.wordpress.com Sampling Design and Procedu Lecture & Seminar
  • 2. If you decide whether or not you want to see a new movie or television program on the basis of the coming attractions or television commercial previews, are you using a sampling technique? A scientific sampling technique?
  • 4. Why Sample? Pragmatic Reasons Accurate and Reliable Results Destruction of Test Units www.mktginc.com
  • 5. Stages in the Selection of a Sample 165
  • 7. Practical Sampling Concepts Defining the Target Population What is the relevant population? Whom do we want to talk to? Population is operationally defined by specific and explicit tangible characteristics. The Sampling Frame A list of elements from which a sample may be drawn; also called working population. Sampling Frame Error Occurs when certain sample elements are not listed or are not accurately represented in a sampling frame.
  • 8. 168 Sampling Units Sampling Unit A single element or group of elements subject to selection in the sample. 1. Primary Sampling Unit (PSU) 2. Secondary Sampling Unit 3. Tertiary Sampling Unit
  • 9. 169 Random Sampling and Non-sampling Errors Random Sampling Error The difference between the sample result and the result of a census conducted using identical procedures. A statistical fluctuation that occurs because of chance variations in the elements selected for a sample. Non-Sampling (Systematic Sampling) Error Systematic (nonsampling) error results from nonsampling factors, primarily the nature of a studys design and the correctness of execution.
  • 10. 1610 Less than Perfectly Representative Samples Random sampling errors and systematic errors associated with the sampling process may combine to yield a sample that is less than perfectly representative of the population. Random Sampling and Nonsampling Errors (contd)
  • 11. Errors Associated with Sampling 1611
  • 13. 1613 Probability Sampling A sampling technique in which every member of the population has a known, nonzero probability of selection. Nonprobability Sampling A sampling technique in which units of the sample are selected on the basis of personal judgment or convenience. The probability of any particular member of the population being chosen is unknown. Probability versus Nonprobability Sampling
  • 15. http://lc.gcumedia.com/hlt362v/the-visual-learner/convenience-sampling.html Nonprobability Sampling: Convenience Sampling Obtaining those people or units that are most conveniently available
  • 16. www.memrise.com Nonprobability Sampling: Judgment (Purposive) Sampling An experienced individual selects the sample based on personal judgment about some appropriate characteristic of the sample member.
  • 17. Nonprobability Sampling: Quota Sampling Ensures that various subgroups of a population will be represented on pertinent characteristics to the exact extent that the investigator desires. BUYERS RESPONDENT QUOTA (SAMPLE SIZE= 200) MEN 40% 80 WOMEN 60% 120
  • 18. Nonprobability Sampling: Snowball Sampling A sampling procedure in which initial respondents are selected by probability methods and additional respondents are obtained from information provided by the initial respondents. slides.com
  • 19. 1619 Probability Sampling Simple Random Sampling Assures each element in the population of an equal chance of being included in the sample. Systematic Sampling A starting point is selected by a random process and then every nth number on the list is selected. Stratified Sampling Simple random subsamples that are more or less equal on some characteristic are drawn from within each stratum of the population.
  • 20. www.nedarc.org Probability Sampling: Simple Random Sampling Assures each element in the population of an equal chance of being included in the sample
  • 21. Probability Sampling : Systematic Sampling A starting point is selected by a random process and then every nth number on the list is selected http://lc.gcumedia.com/hlt362v/the-visual-learner/systematic-sample.html
  • 22. Probability Sampling: Stratified Sampling Simple random subsamples that are more or less equal on some characteristic are drawn from within each stratum of the population http://lc.gcumedia.com/hlt362v/the-visual-learner/stratified-sample.html
  • 23. 1623 Proportional Stratified Sample The number of sampling units drawn from each stratum is in proportion to the population size of that stratum. Disproportional Stratified Sample The sample size for each stratum is allocated according to analytical considerations. Proportional versus Disproportional Sampling
  • 25. 1625 Probability Sampling: Cluster Sampling An economically efficient sampling technique in which the primary sampling unit is not the individual element in the population but a large cluster of elements. Clusters are selected randomly. http://lc.gcumedia.com/hlt362v/the-visual-learner/cluster-sampling.html
  • 26. 1626 Multistage Area Sampling Involves using a combination of two or more probability sampling techniques. Typically, geographic areas are randomly selected in progressively smaller (lower-population) units. Researchers may take as many steps as necessary to achieve a representative sample. Progressively smaller geographic areas are chosen until a single housing unit is selected for interviewing.
  • 28. 1628 What is the Appropriate Sample Design? Degree of accuracy Resources Time Advanced knowledge of the population National versus local project
  • 29. 1629 Internet Sampling is Unique Website Visitors Internet surveys use unrestricted samples. May not be representative. Panel Samples Recruited Ad Hoc Samples
  • 31. Frequency Distribution of Deposits 1731
  • 32. Percentage Distribution of Deposits 1732
  • 34. 1734 Factors of Concern in Choosing Sample Size 1. Variance (or Heterogeneity) A heterogeneous population has more variance (a larger standard deviation) which will require a larger sample. A homogeneous population has less variance (a smaller standard deviation) which permits a smaller sample. 2. Magnitude of Error (Confidence Interval) How precise must the estimate be? 3. Confidence Level How much error will be tolerated?
  • 35. 1735 Sequential Sampling Conducting a pilot study to estimate the population parameters so that another, larger sample of the appropriate sample size may be drawn. Estimating sample size: Estimating Sample Size for Questions Involving Means
  • 36. 1736 Sample Size Example Suppose a survey researcher, studying expenditures on lipstick, wishes to have a 95 percent confident level (Z) and a range of error (E) of less than $2.00. The estimate of the standard deviation is $29.00. What is the calculated sample size?
  • 37. 1737 Sample Size Example Suppose, in the same example as the one before, the range of error (E) is acceptable at $4.00. Sample size is reduced.
  • 38. Calculating Sample Size at the 99 Percent Confidence Level 17-38
  • 39. Determining Sample Size for Proportions 17-39
  • 40. Determining Sample Size for Proportions (contd) 17-40
  • 42. Low Dispersion versus High Dispersion 1742
  • 43. LOs 1. Explain reasons for taking a sample rather than a complete census 2. Describe the process of identifying a target population and selecting a sampling frame 3. Compare random sampling and systematic (nonsampling) errors 4. Identify the types of nonprobability sampling, including their advantages and disadvantages 5. Discuss how to choose an appropriate sample design