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Quality Quiz:Professor Cleary
Another quiz from Professor Cleary

Congratulations: "A" is correct!

Finally, Quinn is right about a sampling concept. (The probability that he would eventually stumble onto a correct application would be the topic for another kind of statistical study.) Berenson Levine Krehbiel’s Basic Business Statistics (Prentice-Hall, ninth edition), a widely-used textbook and one that I adopted for my own classes, defines stratified sample:

“In a stratified sample, the N individuals or items in the frame are first subdivided into separate subpopulations, or strata, according to some common characteristic. A simple random sample is conducted within each of the strata, and the results from the separate simple random samples are then combined. Such sampling methods are more efficient than either simple random sampling or systematic sampling because they ensure representation of individuals or items across the entire population, ensuring a greater precision in the estimates of underlying population parameters. The homogeneity of individuals or items within each stratum, when combined across strata, provides precision.”

A stratified sample can be more efficient than a simple random sample, but the strata must be homogeneous for this to be the case. Further, the strata must be different from each other. Another way to think of this is that the strata should have a great deal of variability between them, but little variability within each stratum.

In this month’s video, I will describe a stratified sample that I utilized as chair of the Parking Committee at Wright State University.

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