Sample Design: Part I
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Dr. Michael R. Hyman, NMSU
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Photographic
Example of
How Sampling
Works
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Sampling Terminology
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Population or universe
Population element
Census
Sample
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Population/Universe
• Any complete group
– People
– Sales territories
– Stores
• Total group from which
information is needed
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Census
Investigation of
all individual
elements that
make up a
population
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Sample
Subset of a larger population of
interest
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Define the target population
Select a sampling frame
Stages in
Selecting
a Sample
Determine if probability or non-probability
sampling method will be chosen
Plan procedure
for selecting sampling units
Determine sample size
Select actual sampling units
Conduct fieldwork
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Define Target Population
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Look at research objectives
Relevant population
Operationally define
Consider alternatives and
convenience
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Select Sampling Frame
• List of elements from which
sample may be drawn
• Mailing and commercial lists can
be problematic (more on this later)
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Sampling Units
• Group selected for the sample
• Can be persons, households,
businesses, et cetera
• Primary sampling units
• Secondary sampling units
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Choose Probability or Nonprobability Sample
• Probability sample
• Known, nonzero probability for every
element
• Non-probability sample
• Probability of selecting any particular
member is unknown
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Conditions Favoring Nonprobability vs. Probability Samples
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Different Sampling Techniques
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Non-probability Samples
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Convenience
Judgment
Quota
Snowball
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Convenience Sample
• Also called haphazard or accidental
sampling
• Sampling procedure for obtaining
people or units that are convenient
to researchers
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Discrepancy between Implied and Ideal
Populations in Convenience Sampling
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Judgment Sample
• Also called purposive sampling
• Experienced person selects sample
based on his or her judgment about
some appropriate characteristics
required of sample members
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Discrepancy
between
Implied and
Ideal
Populations
in Judgment
Sampling
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Quota Sample
• Various population subgroups are
represented on pertinent sample
characteristics to the extent desired by
researchers
• Do not confuse with stratified sampling
(discussed later)
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Representative Quota Sample
Requirements
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Snowball Sample
• Initial respondents selected by
probability methods
• Additional respondents obtained
from information provided by initial
respondents
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