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Chapter10_3

Chapter10_3 - I 586 chapter 10 Introduction to Inference...

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586 chapter 10 Introduction to Inference I Inpt :Data 0: 60 W: 272 n: 840 P:#Po ma 'Po .yi J : , -, 1 1 . 1 1 1 Here are the results of'the z test: z = -1.449 and the P-value is O.Q7\$;6;, . ' . :T ,I:,. , ,* i . If you select "Draw" instead of calculate^ the l?ft dritieal arCa under the normal curve will be shaded and the z-value and P-value will be digplay'ed. -- Po =275. z =-I. 44914 P Value =. 07365 - x ~272. n ~840. 0 =60. i3-,<,Enter=0x' J- MAIN RAD AUTO FUNC 1/1 10.56 CALCULATOR SIGNIFICANCE TESTS (a) Use your calculator in this way to find the z-value and P-value for the true value of the mean p in Example 10.14 (575). Check your calculator findings with the num- bers given in Example 10.14. (b) If you have data, enter the data into any list and then specify a z test. In Example 10.5 (page 546), for example, you would enter the 20 screen tensions into L,/listl. Then from the Z-test screen, specify "Data" and then enter the appropriate values. (c) Use your TI-83/89 to perform the test of significance described in Exercise 10.39 (page 576). 10.3 MAKING SENSE OF STATISTICAL SIGNIFICANCE Significance tests are widely used in reporting the results of research in many fields of applied science and in industry. New pharmaceutical products require

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---- -_ 10.3 Making Sense of Statistical Significance-.---!%? --- - / significant evidence of effectiveness and safety. Courts inquire about statistical significance in hearing class action discrimination cases. Marketers want to know whether a new ad campaign significantly outperforms the old one, and medical researchers want to know whether a new therapy performs significant- ly better. In all these uses, statistical significance is valued because it points to an effect that is unlikely to occur simply by chance. Carrying out a test of significance is often quite simple, especially if you get a P-value effortlessly from a calculator or computer. Using tests wisely is not so simple. Here are some points to keep in mind when using or interpreting sig- nificance tests. Choosing a level of significance The purpose of a test of significance is to give a clear statement of the degree of evidence provided by the sample against the null hypothesis. The P-value does this. But sometimes you will make some decision or take some action if your evidence reaches a certain standard. A level of significance a sets such a standard. Perhaps you will publish a research finding if the effect is significant at the a = 0.01 level. Or perhaps your company will lose a lawsuit alleging racial discrimination if the percent of blacks hired is significantly below the percent of blacks in the pool of potential employees at the a = 0.05 level. Courts have in fact tended to accept this standard in discrimination cases.1° Making a decision is different in spirit from testing significance, though the two are often mixed in practice. Choosing a level a in advance makes sense if you must make a decision, but not if you wish only to describe the strength of your evidence. Using tests with fixed a for decision making is discussed at greater length in Section 10.4.
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Chapter10_3 - I 586 chapter 10 Introduction to Inference...

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