Stat 211 Handout 9 (Chapter 9): Inferences Based on Two Samples tests
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The MINITAB output analyzing such data is N Mean StDev SE Mean B1 8 38479 5590 1976 B2 8 37611 5244 1854 Difference 8 868 1290 456 Test for equal true means in independent samples assuming equal true variances Difference = mu B1 - mu B2 Estimate for difference: 868 95% CI for difference: (-4944, 6681) T-Test of difference = 0 (vs not =): T-Value = 0.32 P-Value = 0.753 DF = 14 Both use Pooled StDev = 5420 Test for equal true means in independent samples assuming unequal true variances Difference = mu B1 - mu B2 Estimate for difference: 868 95% CI for difference: (-4986, 6723) T-Test of difference = 0 (vs not =): T-Value = 0.32 P-Value = 0.754 DF = 13
95% CI for mean difference: (-211, 1948) 99% CI for mean difference: (-728, 2465) T-Test of mean difference = 0 (vs not = 0): T-Value = 1.90 P-Value = 0.099 Test for true means in single samples Test of mu = 3800 vs mu not = 3800 Variable 95.0% CI T P B1 ( 33803, 43156) 17.55 0.000 B2 ( 33224, 41998) 18.24 0.000
F-Test (normal distribution) Test Statistic: 1.136 P-Value : 0.870 Example 11 : An experiment to compare the yield (kg/ha) of Sundance winter wheat and Manitou spring wheat is considered. Data from nine different plots is given in the following table. Is there sufficient evidence to conclude that true average yield for the Sundance winter wheat is more than 500 kg/ha than the Manitou spring wheat? Check the plausibility of any assumptions needed to carry out an appropriate test of hypothesis.
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