Problems: 29.2 6: Which kind of sampling plan was used in each of the following

Question

Problems: 29.2

6: Which kind of sampling plan was used in each of the following situations? Would the plan result in an unbiased sample?

a) Complaints have been made about students not showering after physical education class at a high school. The administration is trying to decide whether to begin requiring showering. They divide the set of interested people into three groups: teachers, students, and parents. A random sample is selected from each group and asked to fill out a brief questionnaire about the need to shower after P.E. class.

b) The managers of a large shopping mall are trying to decide whether to add another information booth to the concourse. They hire a student to stand by one door and ask the next 100 people who enter the mall whether they would like to see another information booth added to the mall and, if so, where.

c) The managers of the new cafeteria on campus want to measure student satisfaction with the new facilities and food offerings. They decide to pass out questionnaires to students who go through the line between the times 8:15 and 8:30, 11:15 and 11:30, 2:15 and 2:30, and 5:15 and 5:30, and ask them to complete the questionnaires. They leave a box at the exit door for completed questionnaires.

d) Three users of the Panther, a new car, reported problems with the trunk lid popping up while driving. SO the car manufacturer test-auto drove the next 30 cars leaving the factory and found that the trunk lid did not pop open. It decided that the problem did not need to be addressed any further.

e) A bookstore is contemplating putting in a coffee bar to attract customers. For three days (December 21-23), they ask each customer who buys a book whether he or she would like to see a coffee bar added to the store.

Explanation / Answer

Part a)

In this case a heterogenous population of teachers , parents and students is first categorized into homogenous groups. These groups are called Stratas. Out of each starta randomly people are selected and the final sample again consists of students , parent s& teachers. Such a sampling is called Stratified sampling . There is no bias is the sample so formed.

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Part b)

Since there is no random selection of sampling units in this case, the sample is shortlisted or formed on the basis of convenience. Such a sampling method is called Convenience sampling. And yes there are chances of it to be biased.

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Part c)

This sample covers different time periods. Suppose the entering of mangers is divided based on time zones. Out of all the available time zones only 4 of them are completely selected. Such a sampling is called Cluster sampling. It may be biased since it fails to cover the population completely.

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Part d)

This is again convenience sampling because the next 30 cars are selected , they may be from the same manufacturing lot and may not have the same defect. It is suggested to include cars from different manufacturing lots into the sample to be tested. That will provide a more convincing result.

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