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Slide 1-2 Chapter 1 The Nature of Statistics Section 1.3 Other Sampling Designs

Slide 1-3 Procedure 1.1 Systematic samples – are obtained by numbering each subject of the populations and then selecting every kth number. For example. If we have 2000 in our population and we need 50 we would then take 2000 ÷ 50 = 40 therefore k = 40. the first subject between 1 and 40 is selected at random. We need to be careful how the subjects in the population are numbered. For example gender – male, female, male, female, etc – every 40 th would be female.

Slide 1-4 Procedure 1.2 Cluster samples - are selected by using intact groups called clusters. Researchers would randomly select some clusters and survey all members. (Geographic area or school district). An example might be apartment dwellers in a large city if we have 10 apartment buildings we might randomly select 2 and interview all members of the apartments.

Slide 1-5 Procedure 1.3 Unfortunately, selecting a sample to be random does not always guarantee that the sample will be representative of the population from which it is drawn. In order to better assure that a sample is representative, statisticians often use a stratified random sample. Stratified samples - The process of drawing a stratified random sample involves, as a first step, dividing the population into stratas (parts) that the researcher feels are important. The sample is then selected by randomly drawing members from each strata. The number drawn from each strata is proportional to the size of the strata. In other words, a stratified random samples is selected by dividing the population into groups (called strata) according to some characteristic that is important to the study, then sampling from each group. Samples within the strata should be randomly selected.

Slide 1-6 Procedure 1.3

Slide 1-7 Summary The four basic methods for obtaining samples are: random, systematic, stratified, and cluster. 7