In many cases a business researcher gathers data to test a hypothesis about a single population mean and the value of the population standard deviation is unknown.In this case the researcher cannot use the z test.

Question

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When the population standard deviation is unknown, the researcher must use the t-test instead of the z-test to test hypotheses about the population mean, as the t-test is designed to account for the added uncertainty of estimating the population standard deviation from the sample.

In Many Cases a Business Researcher Gathers Data to Test