Sampling
9810004M Lydia
9810006M Pippen
Outline
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Sampling strategies: Alternative Paradigms
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External validity
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Defining the population and sample
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Sampling strategies
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Sample size
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Access issues (consent form)
Sampling strategies: Alternative Paradigms
The definition of sampling: select a given number of
people or things from a population.
A: Probability sampling: every member of the population
actually has a possibility of being selected.
B: Nonprobability sampling (purposeful sampling)
theoretical sampling) : select members who had the
particular experience before.
External Validity: Generalization or transferability
Generalize findings to the target (larger) population, so
need to provide sufficient thick description about the case.
Defining the population and sample

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Conceptual definitions: use other constructs to explaining
the meaning.
Operational definitions: specify how the construct will be
measured.
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Through the review studies, the researchers should
formulate a formal, conceptual definition. Ex: target
population=>first-grade students in Taiwan.

Operational definition of the sample (experimentally
accessible population): defined as the list of people who fit
the conceptual definition. Ex: all the first-grade students in
ISU.
Sampling strategies
1.Probability sampling
2.Nonprobability(purposeful) (theoretical)
sampling
3.Conveience sampling
Probability sampling:
1.Simple random sampling
2.Systematic sampling
3.Stratified sampling
4.Cluster sampling
5.Multistage Sampling
1.Simple random sampling:
Each member of the population has an equal and
independent chance of being selected.
pro: it’s a simple process
con: a complete list of the population might not
be available
may include some “outside”.
2.Systematic sampling:
Select every nth name from the population list, so estimate
the needed sample size and dividing the number of the
names on the list by the sample size.
ex:1000/100=10
Pro: not need to have an exact list of all the sampling units.
Con: If the files are arranged in a specific pattern, that
could result in choosing a biased sample.
3.Stratified sampling
A: It used when there are subgroups of different size that
you wish to investigate.
B: Decide the population Into subgroups or levels and then
draw randomly from each subgroup.
Pro: easy to compare each subgroup result
Con: must get information before dividing them
4.Cluster sampling
It is used with naturally occurring groups of individuals.
Ex: city blocks or classroom in a school, and study all the
samples there.
Pro: save time and money by collecting data at a limited
number of sites.
Con: small sample size, less precision in estimating the
effect.
5.Multistage Sampling
Combine sampling strategies.
Ex: cluster sampling +random sampling
Pro: more reliable
Con: complex calculations
 Purposeful
or theoretical sampling
(Nonprobability): the researcher select their
samples with the goal of that allow them to
study a case in-depth.
9.Criterion sampling
1.Extreme or deviant cases
10. Theory-based or operational
2.Intensity sampling
3. Maximum-variation sampling construct sampling
11.Confirming and disconfirming cases
4. Homogeneous sampling
12.Opportunistic sampling
5. Typical-case sampling
6. Stratified purposeful sampling 13.Purposeful random sampling
7. Critical-case sampling
14.Sampling politically important cases
8.Snowball or chain sampling
1.Extreme or deviant cases
The selection of the cases might be to choose individuals
or sites that are unusual or special in some way.
Ex: analyze the highly successful program and compare
them with the fail one.
2.Intensity sampling
It’s similar to the extreme-case strategy, except there is
less emphasis on extreme.
Explore rich information on the typical cases.
3. Maximum-variation sampling
Maximize the variation within the sample and indicate their
major difference.
EX: The study of students’ English ability in different
location( rural, urban)
4. Homogeneous sampling
The researcher seeks to describe the experience of
subgroups of people who share similar characteristics.
EX: rural teachers’ attitude toward CLT for children.
5. Typical-case sampling
A: Choose the case in which a program has been
implemented to show this case is indeed average.
B: It is like Intensity sampling.
6. Stratified purposeful sampling
A: It’s a combination of sampling strategies.
B: Subgroups are chosen on specified criteria
a sample of cases is selected within those strata.
7. Critical-case sampling
A: Study a very important, critical case.
B: The effect should be representative.
8.Snowball or chain sampling
The research starts with a key person and introduce the
next one to become a chain.
9.Criterion sampling
The researcher set up a criterion and identify cases that
meet that criterion.
Ex: study cases that could pass TOEFL last semester
10.Theory-based or operational construct sampling:
A: Define a theoretical construct
B: Select the sample who have really that kind of
experiment
Ex: metacognitive learning on EFL reading development
11. Confirming and disconfirming cases:
After analyzing sample cases, the researcher has to
form grounded theory that fit (confirming) and do not fit
(disconfirming) the major points in the literature.
12. Opportunistic sampling:
A: The researcher should make a decision on the spot as
to the relevance of the activity.
B: Take the opportunity to decide the sampling procedure
or samples during the study.
13. Purposeful random sampling:
A: To choose those who will be included in a very small
sample.
B: Randomly select participants who had similar
experiences in a very small sample
14. Sampling politically important cases:
The rationale rests on the perceived credibility of the
study by the person expected to use the results. (Use
particular samples)
Ex: KMT DPP

Example of qualitative research sampling
Convenience sampling:
Convenience sampling means that the persons
participating in the study were chosen because they were
readily available.
EX: Neighbors, friends
Pros and Cons of purposeful sampling and
Convenience sampling:
Pro: 1. Spend less cost and time
2. Ease of administration
3. Assures high participation rate
4. Generalization possible to similar subject
5. ( Assures receipt of needed information)
Con:1. Difficult to generalize to other subjects
2. Less representative of an identified population
3. Greater subject bias
Access issues
A. Get permission and agreement with the appropriate
person (e.g., school principal, classroom teacher, or
parents)
B. Obtain consent form from the participants
C. How to “label” students if using stratified sampling
D. Consider appropriate sample size
Sample Size:
For different types of research, rule of thumb can be used
to determine the appropriate sample size.
Rules of thumb:
A: Quantitative research rules of thumb:
For survey research needs 100 cases.
B: Qualitative research rules of thumb:
For grounded theory needs30~50 interviews.
Access to records
Consent form:
A. Explain research purpose, duration, and procedures
B. Describe any risk or discomfort
C. Describe confidentiality or anonymity
D. Provide the name of person to contact with
E. Provide voluntary participation, and available to
refuse or withdraw any time