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# Ch24 - Difference between Means • We test the hypothesis...

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Chapter 24 Comparing Means

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2 Sample t-Interval for the Difference between Means When the conditions are met, we are ready to find the confidence interval for the difference between means of 2 independent groups, . The confidence interval is where 2 1 μ μ - ) ( SE ) ( 2 _ 1 _ * 2 _ 1 _ y y t y y df - ± - 2 2 2 1 2 1 _ 2 _ 1 ) y y SE( n s n s + = -
Degrees of Freedom? The degrees of freedom is always at least the smaller of the two n’s minus 1 and at most the sum of the two n’s minus 2. The degrees of freedom that I most commonly use is . 2 n n 2 1 - +

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Actual Degrees of Freedom 2 2 2 2 2 2 1 2 1 1 2 2 2 2 1 2 1 n s 1 n 1 n s 1 n 1 n s n s df - + - + =
Work on #12 on p. 641

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Unformatted text preview: Difference between Means • We test the hypothesis using the statistic : H 2 1 =- μ μ -- -= _ 2 _ 1 _ 2 _ 1 y y SE y y t Standard Error for Hypothesis Testing • Unlike the standard error for difference of proportions, the standard error for difference of means is the same as the confidence interval. What about Pooled Data? • We can do a pooled t-test for the difference between the means of 2 independent groups but we will not be covering it. Work on #31 on p. 646...
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Ch24 - Difference between Means • We test the hypothesis...

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