lecture_7_2

# lecture_7_2 - Inference for distributions Comparing two...

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Inference for distributions: Comparing two means IPS chapter 7.2 © 2006 W.H. Freeman and Company

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Objectives (IPS chapter 7.2) Comparing two means Two independent samples t -distribution Two sample t -test Two-sample t -confidence interval
Does smoking damage the lungs of children exposed to parental smoking? Forced vital capacity (FVC) is the volume (in milliliters) of air that an individual can exhale in 6 seconds. FVC was obtained for a sample of children not exposed to parental smoking and a sample of children exposed to parental smoking. We want to know whether parental smoking decreases children’s lung capacity as measured by the FVC test. Is the mean FVC lower in the population of children exposed to parental smoking? Parental smoking s n Yes 75.5 9.3 30 No 88.2 15.1 30 x

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Comparing two samples Which is it? We often compare two treatments used on independent samples. Is the difference between both treatments due only to variations from the random sampling (B), or does it reflects a true difference in population means (A)? Independent samples: Subjects in one samples are completely unrelated to subjects in the other sample.
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