lec6.5 - 155 Lecture 16: CHAPTER 6: HYPOTHESIS TESTING...

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Lecture 16: CHAPTER 6: HYPOTHESIS TESTING Large-Sample Tests for the Difference Between Two Means (Section 6.5, page 418) So far, we’ve only been looking at a single mean, it’s now time to extend our knowledge of hypothesis tests on 2 means. Specifically, two means which come from large sample sizes. Our formulas start to change, as well as our hypothesis. We now investigate examples in which we wish to determine whether the means of two populations are equal. As an example to set up a hypothesis: Suppose that a production manager for a manufacturer of industrial machinery is concerned that ball bearings produced in environments with low ambient temperatures may have smaller diameters than those produced under higher temperatures. Set up the hypothesis: To investigate this concern, she samples 120 ball bearings that were manufactured early in the morning, before the shop was fully heated, and finds their mean diameter to be 5.068 mm and their standard deviation to be 0.011 mm. She independently samples 65 ball bearings manufactured during the afternoon and finds their mean diameter to be 5.072 mm and their standard deviation to be 0.007 mm. Can she conclude that ball bearings manufactured in the morning have smaller diameters, on average, than ball bearings manufactured in the afternoon? 2
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lec6.5 - 155 Lecture 16: CHAPTER 6: HYPOTHESIS TESTING...

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