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.

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

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

See example on the bottom of page 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

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 10 th grade students, all elementary school gifted children in Utah

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)

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

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.

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

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

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

Systematic Sampling Steps in Systematic Sampling

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

Selecting a nonrandom sample Nonprobability or nonrandom sample Convenience sampling Purposive sampling Quota sampling

Qualitative Sampling: Definition and Purpose

Task # 4: Performance Criteria