slide 7.1 saunders, lewis and thornhill, research methods for business students, 5 th edition, ©...
TRANSCRIPT
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Slide 7.1
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Chapter 7Selecting Samples
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Slide 7.2
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Selecting samplesPopulation, sample and individual cases
Source: Saunders et al. (2009)
Figure 7.1 Population, sample and individual cases
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Slide 7.3
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
The need to sample
Sampling- a valid alternative to a census when
• A survey of the entire population is impracticable
• Budget constraints restrict data collection
• Time constraints restrict data collection
• Results from data collection are needed quickly
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Slide 7.4
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Overview of sampling techniquesSampling techniques
Source: Saunders et al. (2009)Figure 7.2 Sampling techniques
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Slide 7.5
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Probability sampling
The four stage process
1. Identify sampling frame from research objectives
2. Decide on a suitable sample size
3. Select the appropriate technique and the sample
4. Check that the sample is representative
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Slide 7.6
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Identifying a suitable sampling frame
Key points to consider
• Problems of using existing databases
• Extent of possible generalisation from the sample
• Validity and reliability
• Avoidance of bias
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Slide 7.7
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Sample size
Choice of sample size is influenced by• Confidence needed in the data
• Margin of error that can be tolerated• Margin of error (also called The confidence interval ) is the plus-or-minus
figure usually reported in newspaper or television opinion poll results. For example, if you use a margin of error of 4 and 47% percent of your sample picks an answer you can be "sure" that if you had asked the question of the entire relevant population between 43% (47-4) and 51% (47+4) would have picked that answer.
• Types of analyses to be undertaken
• Size of the sample population and distribution
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Slide 7.8
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
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Slide 7.9
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
The importance of response rate
Key considerations
• Non- respondents and analysis of refusals
• Obtaining a representative sample
• Calculating the active response rate
• Estimating response rate and sample size
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Slide 7.10
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Selecting a sampling technique
Five main techniques used for a probability sample
• Simple random
• Systematic
• Stratified random
• Cluster
• Multi-stage
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Slide 7.11
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Simple random sampling
• Number each of the cases in your sampling frame with a unique number.
• Select cases using random numbers until, actual sample size is reached.
• Computer aided telephone interviewing (CATI) software
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Slide 7.12
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Systematic Random Sampling
• Number each of the cases in your sampling frame with a unique number.
• Select the first case using a random number• Calculate the sampling fraction• Select subsequent cases systematically using the
sampling fraction to determine the frequency of selection.
• Sampling fraction = actual sample size/ total population
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Slide 7.13
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Stratified random sampling
• Choose the stratification variable or variables
• Divide the sampling frame into the discrete strata.
• Number each of the cases within each stratum with a unique number
• Select your sample using either simple random or systematic random sampling
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Slide 7.14
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Cluster sampling
• Choose the cluster grouping for your sampling frame.
• Number each of the clusters with a unique number.
• Select sample of clusters using random sampling
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Slide 7.15
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Multi-stage sampling
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Slide 7.16
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Non- probability sampling (1)
Key considerations
• Deciding on a suitable sample size– Data saturation
• Selecting the appropriate technique
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Slide 7.17
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Non- probability sampling (2)
Sampling techniques
• Quota sampling (larger populations)
• Purposive sampling
• Snowball sampling
• Self-selection sampling
• Convenience sampling
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Slide 7.18
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Quota Sampling
• Divide the population into specific groups.
• Calculate quota for each group based on relevant and available data
• Collect data from each quota
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Slide 7.19
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Purposive sampling
• Extreme case/deviant sampling: unusual or special case enable to learn the most about the RQ.
• Heterogeneous or maximum variation sampling: representing different subgroups
• Homogeneous sampling: One subgroup.
• Critical case sampling: – If it happen there, it will happen everywhere.
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Slide 7.20
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Snowball sampling
• Make contact with one or two cases in the population.
• Ask these cases to identify further cases.
• Ask these new case to identify further new cases.
• Stop when either no new cases are given or the sample is large enough.
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Slide 7.21
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Self select sampling
• Publicize your need for cases
• Collect data from those who respond
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Slide 7.22
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Haphazard sampling
• Also called purposive or availability sampling.
• Select case based on ease or convenience.
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Slide 7.23
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Summary: Chapter 7
• Choice of sampling techniques depends upon the research question(s) and their objectives
• Factors affecting sample size include:
- confidence needed in the findings
- accuracy required
- likely categories for analysis
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Slide 7.24
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Summary: Chapter 7
• Probability sampling requires a sampling frame and can be more time consuming
• When a sampling frame is not possible, non- probability sampling is used
• Many research projects use a combination of sampling techniques
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Slide 7.25
Saunders, Lewis and Thornhill, Research Methods for Business Students, 5th Edition, © Mark Saunders, Philip Lewis and Adrian Thornhill 2009
Summary: Chapter 7
All choices depend on the ability to gain access to organisations