511_Chap3 - A Closer Look at Assumptions Stat 511 Chapter 3...

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A Closer Look at Assumptions Stat 511 Chapter 3
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Cloud Seeding Experiment – Case Study 1 Cloud seeding to increase rainfall (randomized experiment) 52 cumulus clouds At random 26 were seeded and 26 were controls Experimenter and pilot were ‘blind’ to the treatment
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-500 0 500 1000 1500 2000 2500 3000 RAINFALL SEEDED UNSEEDED TREATMENT
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Data Characteristics Data were positively skewed, and the group with the higher center also had the higher spread Log transformation of rainfall was used
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-1 0 1 2 3 4 5 6 7 8 lograin SEEDED UNSEEDED TREATMENT
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Analysis of Log Data One-sided p-value for two-sample t-test was 0.007 Seeded clouds had 3.1 times as much rainfall as the unseeded 95% confidence interval for this ratio is 1.3 to 7.7 What is our scope of inference?
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Effects of Agent Orange on Troops in Vietnam (Observational Study) 646 Vietnam veterans and 97 other veterans Neither sample was randomly selected Similar shape and spread Scope of inference?
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Dioxin Concentration for Veterans 0 10 20 30 40 DIOXIN OTH ... VIETNAM VETERAN Vet #645 Vet #646
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All Data Two Sample T-Test and Confidence Interval data: x: DIOXIN with VETERAN = OTHER , and y: DIOXIN with VETERAN = VIETNAM t = -0.263, df = 741, p-value = 0.7926 alternative hypothesis: true difference in means is not equal to 0 95 percent confidence interval: -0.6305128 0.4815229 sample estimates: mean of x mean of y 4.185567 4.260062
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Drop Veteran 646 Two Sample T-Test and Confidence Interval data: x: reduced1 with VETERAN = OTHER , and y: reduced1 with VETERAN = VIETNAM t = -0.0489, df = 740, p-value = 0.961 alternative hypothesis: true difference in means is not equal to 0 95 percent confidence interval: -0.4662617 0.4435973 sample estimates: mean of x mean of y 4.185567 4.196899
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Also Drop Veteran 645 Two Sample T-Test and Confidence Interval data: x: reduced2 with VETERAN = OTHER , and y: reduced2 with VETERAN = VIETNAM t = 0.0969, df = 739, p-value = 0.9228 alternative hypothesis: true difference in means is not equal to 0 95 percent confidence interval: -0.4038465 0.4457879 sample estimates: mean of x mean of y 4.185567 4.164596
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