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Sample Surveys Study Guide (page 4)

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Updated on Oct 5, 2011

Example

In each question, identify whether the sample is a stratified random sample or a cluster sample.

  1. A large school system decided to survey sophomores within its high schools. Three schools were randomly selected, and all sophomores in those schools were included in the sample.
  2. A professional society wants to improve its member services. It takes a simple random sample of current members and another simple random sample of members who have chosen not to renew. All people selected are surveyed.

Solution

  1. This sampling plan leads to a cluster sample. The schools are the clusters, which are randomly selected. The sophomores within each school are the cluster members.
  2. This sampling plan results in a stratified sample. There are two strata: current members and members who have not renewed their membership. A simple random sample is selected within each stratum.

Sample Surveys In Short

Sample surveys are very useful for estimating the proportion of population units with a specific trait or opinion. Selecting a sample that allows us to make unbiased estimates of this proportion is challenging. Simple random sampling is appealing and leads to simple estimates, but selecting a true simple random sample may be physically impossible. For large surveys, stratified random samples, cluster samples, systematic samples, or a combination of these in a multistage sample may be easier to implement, more cost effective, and produce good estimates. Random-digit dialing approximates a simple random sample of all households with telephones in the region of interest.

Find practice problems and solutions for these concepts at Sample Surveys Practice Exercises.

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