511_Chap3

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

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Unformatted text preview: A Closer Look at Assumptions Stat 511 Chapter 3 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-500 500 1000 1500 2000 2500 3000 RAINFALL SEEDED UNSEEDED TREATMENT Data Characteristics Data were positively skewed, and the group with the higher center also had the higher spread Log transformation of rainfall was used-1 1 2 3 4 5 6 7 8 lograin SEEDED UNSEEDED TREATMENT 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? 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? Dioxin Concentration for Veterans 10 20 30 40 DIOXIN OTH ... VIETNAM VETERAN Vet #645 Vet #646 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 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 Also Drop Veteran 645 Two Sample T-Test and Confidence Interval data: x: reduced2 with VETERAN = OTHER , and y: reduced2 with VETERAN = VIETNAM...
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511_Chap3 - A Closer Look at Assumptions Stat 511 Chapter 3...

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