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8/3/2019 Sampling BPT
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Explain the role of sampling in theresearch process
Distinguish between probability and
nonprobability sampling Understand the factors to consider
when determining sample size
Understand the steps in developing a
sampling plan
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Sampling is the process
of selecting a small number of elements
from a larger defined target group
of elements such that
the information gathered
from the small group will allow judgments
to be made about the larger groups
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Sampling error is any type of bias
that is attributable to mistakesin either drawing a sample or
determining the sample size
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1. Define the Population of Interest2. Identify a Sampling Frame (if possible)
3. Select a Sampling Method
4. Determine Sample Size5. Execute the Sampling Plan
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Population of interest is entirely dependenton Management Problem, Research Problems,and Research Design.
Some Bases for Defining Population:◦ Geographic Area
◦ Demographics
◦ Usage/Lifestyle
◦ Awareness
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A list of population elements (people,companies, houses, cities, etc.) from whichunits to be sampled can be selected.
Difficult to get an accurate list. Sample frame error occurs when certain
elements of the population are accidentallyomitted or not included on the list.
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Probabilitysampling
Nonprobabilitysampling
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Probability
Simple randomsampling
Systematic randomsampling
Stratified randomsampling
Cluster sampling
Nonprobability
Conveniencesampling
Judgment sampling Quota sampling
Snowball sampling
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Simple random sampling is a method of
probability sampling in whichevery unit has an equal nonzero
chance of being selected
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Systematic random sampling is a
method of
probability sampling
in which the defined
target population is ordered
and the sample is selected
according to position using a skip interval
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1: Obtain a list of units that contains anacceptable frame of the target population
2: Determine the number of units in the listand the desired sample size
3: Compute the skip interval 4: Determine a random start point 5: Beginning at the start point, select the
units by choosing each unit thatcorresponds to the skip interval
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Stratified random sampling is a
method of
probability samplingin which the population is divided
into different subgroups and samples
are selected from each
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1: Divide the target population intohomogeneous subgroups or strata
2: Draw random samples fro each stratum
3: Combine the samples from each stratuminto a single sample of the targetpopulation
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Convenience sampling reliesupon convenience and access
Judgment sampling relies upon beliefthat participants fit characteristics
Quota sampling emphasizes representationof specific characteristics
Snowball sampling relies upon respondentreferrals of others with like characteristics
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Research objectives Degree of accuracy
Resources Time frame
Knowledge oftarget population Research scope
Statistical analysis needs
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How many completed questionnaires do weneed to have a representative sample?
Generally the larger the better, but that takesmore time and money.
Answer depends on:◦ How different or dispersed the population is.
◦ Desired level of confidence.
◦ Desired degree of accuracy.
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Common Methods:◦ Budget/time available
◦ Executive decision
◦ Statistical methods◦ Historical data/guidelines
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Variability of the population characteristicunder investigation
Level of confidence desired in the estimate
Degree of precision desired in estimatingthe population characteristic