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Looking at Confidence Interval Critical Values

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2016-03-26 7:39:19
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Statistics All-in-One For Dummies
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Critical values (z*-values) are an important component of confidence intervals (the statistical technique for estimating population parameters). The z*-value, which appears in the margin of error formula, measures the number of standard errors to be added and subtracted in order to achieve your desired confidence level (the percentage confidence you want).

The following table shows common confidence levels and their corresponding z*-values.

Confidence Level z*-value
80% 1.28
85% 1.44
90% 1.645
95% 1.96
98% 2.33
99% 2.58

You can also use these critical z*-values for hypothesis tests in which the test statistic follows a Z-distribution. If the absolute value of the test statistic is greater than the corresponding z*-value, then reject the null hypothesis.

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About the book author:

Deborah J. Rumsey, PhD, is an Auxiliary Professor and Statistics Education Specialist at The Ohio State University. She is the author of Statistics For Dummies, Statistics II For Dummies, Statistics Workbook For Dummies, and Probability For Dummies.

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