Sampling Procedures

Topics Covered in this Session

Sampling

Definition – sampling is selecting a group (subgroup) from a much larger population that is similar in its trait (i.e. gender, ethnicity, age, income, etc.) distribution of the larger population. Findings made from studying the group can then be generalized to the larger population.
Depending on the methodology being used in a study, sampling a population may or may not be necessary. Studies that limit themselves to describing activity for a specific population do not have to use sampling techniques but can accept whatever sample is available. This is frequently the case with historical, ethnographic, action and evaluation research.
However, studies that attempt to infer that the findings from a sample can be extended to a larger population need to establish that the sample is representative of the larger population. Representation here refers to the basic trait distribution of a population. For example, if a general population is made up of 51% females and 49% males, a sample (regardless of size) that is made up of 58% females and 42% males is not representative on this trait

Sampling Techniques

Various sampling techniques can be used depending on the type of research to be conducted. The two major types of techniques are probability sampling and nonprobability sampling.

Sample Sizes

There is an extensive literature base on sample sizes. However, overall agreement on sample sizes is elusive. The basic assumption that the larger the sample the more representative of the population is not always the case. This is frequently true when the sample size is improperly selected or controlled. Many researchers hold that the accuracy of a sample is more important than the size. On the other hand, when using certain statistical procedures such correlation coefficients or analysis of variance, minimal sample sizes are recommended for the statistical significance to be valid. A broad rule of thumb is that samples smaller than 30 subjects are not likely to reflect the trait distributions that exist in a population.

FOR MORE INFORMATION ON THE TOPICS COVERED IN THIS SESSION, PLEASE REFER TO CHAPTER 1 OF A.G. PICCIANO "EDUCATIONAL RESEARCH PRIMER".