For each of the following, identify which type of sampling is represented.
Students in your class are divided into females and males. A random sample of size 5 is then drawn from each of the groups.
You are interested in estimating the average number of hours dormitory residents spend studying. In each dormitory, one floor is chosen at random and all the students on that floor are interviewed.
You are researching the proportion of college students who prefer country music to other forms of music. You obtain a listing of all the students at your college and contact every 20th student on the list.
Your campus statistical consulting center uses random digit dialing to locate potential subjects for a political survey.
A student is investigating the prevalence of flu on campus this semester, and he asks 20 of his friends whether they have had the flu.
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Solution
Stratified sampling: (a) the population was divided into subgroups (females and males), and (b) a random sample was drawn from each of the groups.
Cluster sampling: (a) the population was divided into clusters (dormitory floors), (b) a random sample of the clusters (floors) is taken, and (c) all students on that floor (cluster) were selected.
Systematic sampling: where every th member of the population is taken, with .
An example of random sampling, as illustrated on page 21.
Convenience sampling: the student is choosing a sample convenient for him.