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Unformatted text preview: 1 STA2023 Chapter 21 (More About Tests) Skip: Critical Values Again (pg. 539540), Power (545546), A Picture is WorthWords (547548), Reducing Type I and Type II Errors (548549) In chapter 20 you learned that one should reject H (and support H A ) only when the pvalue is small. But, what is small enough? The level of significance ( ) is used to define a threshold for when a pvalue is small enough. Note that this level of significance should be chosen before collecting your data and running your hypothesis test (page 538539). If not, you might be accused of cheating. In everyday practice it is common to use alpha levels of 0.10, 0.05, or 0.01 pvalue , Reject H and Support H A ( statistically significant test results) pvalue > , Fail to Reject H and Do Not Support H A (results are not statistically significant ) Beware that the level of significance is often just an arbitrarily chosen threshold level. As such, in the real world, it should only be used as a guide in determining whether or not the test results are statistically significant. Recall that the previous chapter prompted you to always include the pvalue in your conclusion statement of a hypothesis test. Perhaps now you see why the pvalue is the true measure that defines the strength of the evidence against the null hypothesis (H ) and in favor of the alternative hypothesis (H A ). Activity 1: Lets say that we wanted to run a hypothesis test to determine if the percentage of all students currently passing this course (all instructors, not just me) is below 70%. H : p = 0.70 H A : p < 0.70 From a random sample of n = 87 students, it was found that only 54 are currently passing....
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This note was uploaded on 11/22/2010 for the course STA 2023 taught by Professor Ripol during the Spring '08 term at University of Florida.
 Spring '08
 Ripol
 Statistics

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