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Ch. 16 SAMPLING DESIGNS
AND SAMPLING PROCEDURES
www.wernermurhadi.wordpress.com
Dr. Werner R. Murhadi
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Sampling Terminology
Sample is a subset, or some part, of a larger population.
population (universe) is any complete group of entities that share
some common set of characteristics.
population element is an individual member of a population.
Census is an investigation of all the individual elements that make up a
population.
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Why Sample?
Pragmatic Reason: Applied
business research projects
usually have budget and time
constraints.
Accurate and Reliable
Results: see figure
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Practical Sampling Concepts
sampling frame
A list of elements from which a
sample may be drawn; also
called working population.
sampling unit
A single element or group of
elements subject to selection in
the sample.
LOGORandom Sampling and
Nonsampling Errors
Random sampling error is The difference between the
sample result and the result of a census conducted using
identical procedures.
Random sampling error is a function of sample size. As
sample size increases, random sampling error
decreases.
Systematic (nonsampling) errors result from
onsampling factors, primarily the nature of a study’s
design and the correctness of execution.
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Total Error
Random Sampling Error,
occur because the particular
sample selected is an
imperfect representation
of the population of interest
Nonsampling Error
Response Error Nonresponse Error
Researcher Error Interviewer Error Respondent Error
Surrogate Information Error
Measurement Error
Population Definition Error
Sampling Frame error
Data Analysis error
Respondent Selection Error
Questioning Error
Recording Error
Cheating error
Inability Error
Unwillingness Error
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Sampling frame errors eliminate some potential respondents.
Random sampling error (due exclusively to random, chance
fluctuation) may cause an imbalance in the representativeness of
the group.
Additional errors will occur if individuals refuse to be interviewed
or cannot be contacted.
LOGOProbability versus
Nonprobability Sampling
probability sampling is A sampling technique in which
every member of the population has a known, nonzero
probability of selection.
nonprobability sampling is 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.
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Sampling technique
Nonprobability Probability
Convenience/
Haphazard/
Accidental
Judgmental/
Purposive
Quota Snowball
Simple Random Systematic Stratified Cluster Others
Proportionate Disproportionate
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Convenience Sampling
Also called haphazard or accidental
sampling
The sampling procedure of obtaining
the people or units that are most
conveniently available (people passing
in a mall).
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Judgment Sampling
Also called purposive sampling
An experienced individual selects the
sample based on his or her judgment
about some appropriate characteristics
required of the sample member (CPI
Consumer Price Index).
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Quota Sampling
Ensures that the various subgroups in
a population are represented on
pertinent sample characteristics (Brand
of DVD owners ie. Sony, Samsung,
Toshiba )
To the exact extent that the
investigators desire
It should not be confused with stratified
sampling.
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Snowball Sampling
A variety of procedures
Initial respondents are selected by
probability methods
Additional respondents are obtained
from information provided by the initial
respondents (Buyers of more than 50
DVDs per year).
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Simple Random Sampling
A sampling procedure that ensures that
each element in the population will have
an equal chance of being included in
the sample (Lottery)
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Systematic Sampling
A simple process
Initial random point
Every n-th name from the list will be
drawn
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Stratified Sampling
Probability subsample in each strata
Subsamples are drawn within different
strata or groups
Each stratum is more or less equal on
some characteristic
Do not confuse with quota sample
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Cluster Sampling
The purpose of cluster sampling is to
sample economically while retaining the
characteristics of a probability sample.
The primary sampling unit is no longer
the individual element in the population
(ie. Cities, universities, career)
The primary sampling unit is a larger
cluster of elements located in proximity
to one another
LOGOWhat is the
Appropriate Sample Design?
Degree of accuracy
Resources
Time
Advanced knowledge of the population
National versus local
Need for statistical analysis