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Lecture 13S

# Lecture 13S - Statistics 371-001 Sp 09 Lecture#13 5 Mar 09...

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y y Statistics 371-001, Sp 09 Lecture #13 5 Mar 09 Chapter 7. Comparison of Two Independent Samples 7.3 Confidence Interval for the Difference Between two . Recall, to place 95% confidence interval around a μ : use To place 95% confidence interval around , use First, to find t value for 95% from Table 4, need df . or df = ( n 1 + n 1 – 2) Example: Physiologist evaluates effect of hormone X on feeding behavior in rats. Food consumed, mg Group 1 Group 2 Placebo Hormone X 8 5 10 6 12 3 6 4 6 7 7 8 9 6 8 5 7 4 11 8 P = 8.4 H =5.6 n P = 10 n H = 10

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s P 2 s H 2 = 4.27 = 2.93 Note: This is the sample variance . Using pooled SE df = ( n 1 + n 1 – 2) = (10 + 10 – 2) =18 t 0.025 (df=18) = 2.101 mg, (1.02, 4.58) We are 95% confident that rats consume between 1.02 to 4.58 mg more when given hormone X compared to placebo. The probability is .95 that the confidence interval between 1.02 and 4.58 mg contains the mean difference food consumption for how much more rats given hormone X consumed relative to placebo controls. Same problem using added variance for SE Lecture 13 page 2
t 0.025 (df=24.16) ~ 2.064 mg, (1.05, 4.55) 2. Hypothesis Testing Another inferential statistics procedure.

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