Sampling

9810004M Lydia

9810006M Pippen

Outline

Sampling strategies: Alternative Paradigms

External validity

Defining the population and sample

Sampling strategies

Sample size

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

Conceptual definitions: use other constructs to explaining the meaning.

Operational definitions: specify how the construct will be measured.

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.

1.Extreme or deviant cases

2.Intensity sampling

3. Maximum-variation sampling

4. Homogeneous sampling

5. Typical-case sampling

6. Stratified purposeful sampling

7. Critical-case sampling

8.Snowball or chain sampling

9.Criterion sampling

10. Theory-based or operational

construct sampling

11.Confirming and disconfirming cases

12.Opportunistic sampling

13.Purposeful random sampling

14.Sampling politically important cases

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