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# ex17ans - STAT 420 Examples#17 Spring 2008 1 We wish to...

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STAT 420 Examples #17 Spring 2008 1. We wish to test whether coffee stunts the growth of children. We obtain a random sample of 6 adult males who started drinking coffee regularly before the age of 14, and a random sample of 8 adult males who did not drink coffee regularly before the age of 14. The heights of the 14 individuals in inches are as follows: Coffee: 65, 68, 67, 66, 71, 68. No Coffee: 68, 70, 67, 71, 70, 72, 73, 69. Assume that the populations are approximately normally distributed, and that the overall variances are equal. a) Compute 1 y , 2 y , 2 1 s , and 2 2 s . n = 6 m = 8 6 405 = = n x x = 67.5 8 560 = = m y y = 70 x x x - ( ) 2 x x - y y y - ( ) 2 y y - 65 2.5 6.25 68 2 4 68 0.5 0.25 70 0 0 67 0.5 0.25 67 3 9 66 1.5 2.25 71 1 1 71 3.5 12.25 70 0 0 68 0.5 0.25 72 2 4 0 21.5 73 3 9 69 1 1 0 28 ( ) 5 5 . 21 1 2 2 1 = = - - n x x s = 4.3 ( ) 7 28 1 2 2 2 = = - - m y y s = 4

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b) Test for difference in the average heights for these two groups using the t test and pooled variance. Use a 5% level of significance. What can you say about the p-value of this test? ( ) ( ) 2 1 1 2 1 2 2 2 2 1 1 2 pooled - + - + - = n n s n s n s To test H 0 : μ 1 μ 2 = δ 0 Assumptions: 1) Both populations are normal. 2) The population standard
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ex17ans - STAT 420 Examples#17 Spring 2008 1 We wish to...

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