CHAPTER 4: SELECTING A SAMPLE

2. CHAPTER 4: SELECTING A SAMPLE • Identify and describe four random sampling techniques. • Select a random sample using a table of random numbers. • Identify three variables that can be stratified. • Select stratified samples, cluster samples, and systematic samples. • Identify and describe three nonrandom sampling techniques. • Identify and briefly describe two major sources of sample bias. • Describe quantitative and qualitative sampling strategies.

3. Sampling- • the process of selecting a number of participants for a study in such a way that they represent the larger group from which they were selected

4. Sample- • comprises the individuals, items, or events selected from a larger group referred to as a population • If a quantitative sample is selected, the research results on it will be generalizable to the population. • If a qualitative sample is selected, it will likely focus on a limited group of articulate participants

5. See example on the bottom of page 102. • -500 teachers were selected to discuss what they felt about teacher unions • -Conclusions based on intervies • -How about 500 teachers who are members of the NEA? • -There are several relatively simple sampling techniques that could be applied to represent a sample of teachers

6. Defining a Population • Population- • is the group of interest to the researcher, the group to which the results of the study will ideally generalize. • Ex.—all 10th grade students, all elementary school gifted children in Utah

7. Defining a Population • Target population- • the population that the researcher would ideally like to generalize to • Available (accessible) population- • the population that the researcher can realistically select from • -It is important to define your population in sufficient detail so that others may determine how applicable your findings are to their situation. • -Regardless of what sampling approach is used, it should describe the characteristics of the sample. (i.e.- the number of participants, the demographics, percentage of each racial and gender group, level of education, achievement level)

8. Selecting a Random Sample • -Very important step in conducting a research study for quantitative research • -Selecting a representative sample is not a haphazard process

9. The steps are same: • Identify the problem • Determine the required sample size • Select the sample • Four basic random sampling techniques: • simple random sampling • stratified sampling • cluster sampling • systematic sampling • Probability sampling- • it is possible for the researcher to specify the probability, or chance, that each member of a defined population will be selected for the sample.

10. Steps in Simple Random Sampling • Selecting a sample involves the following steps: • An Example of Random Sampling

11. Stratified Sampling • Subgroup or strata- a variable that can be divided into groups • Steps for Equal-Sized Groups in Stratified Sampling • An Example of Proportional Stratified Sampling

12. Cluster Sampling • Cluster- any population where we find an intact group of similar characteristics

13. Systematic Sampling • Steps in Systematic Sampling

14. Determining Sample Size • (see table 4.2) Samples sizes (S) required for given populations (N) • Avoiding Sampling Error and Bias

15. Selecting a nonrandom sample • Nonprobability or nonrandom sample • Convenience sampling • Purposive sampling • Quota sampling

16. Qualitative Sampling: Definition and Purpose

17. Task # 4: Performance Criteria