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Course Documents

Chapter 1 - Intro

Chapter 2 - Methods for Describing Sets of Data

Chapter 3 - Probability

Chapter 4 - Discrete Random Variables

Chapter 5 - Normal Random Variables

Chapter 6 - Sampling Distributions

Chapter 7 - Confidence Intervals

Chapter 8 - Tests of Hypothesis: One Sample

Chapter 9 - Confidence Intervals and Hypothesis Tests: Two Samples

Sample Exam I: Chapters 1 & 2

Sample Exam II: Chapters 3 & 4

Sample Exam III: Chapters 5 & 6

Sample Exam IV: Chapters 7 & 8

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Recently asked questions for category: Conf. Interval: Two Indep. Means

A Stats Professor student asks:

In the video for example 135, you state that it doesn't really matter which we take as X1 or X2 (the weight watchers or the atkins). Well, I worked out the problem with you, having done the opposite calculation (you got -.9, I got .9 because I subtracted weight watchers from atkins instead of atkins from weight watchers).

The confidence interval I got had the same numbers but different signs:

Your confident interval in the video: [-3.85,1.78]
My confidence interval: [-.178, 3.85]
I worked everything else out with you in the same manner (t alpha/2, s2p, and E).

My question is if there should be a certain way that we evaluate these problems to determine which will be x bar #1 (X1) and which will be x bar #2 (X2). I don't want to calculate any which way and get the confidence interval wrong on the exam.

Here is example 135: Among 28 subjects using the Weight Watchers diet, the mean weight loss after a year was 3.0 pounds with a standard deviation of 4.9 pounds. Among 25 subjects using the Atkins diet, the mean weight loss after one year was 2.1 pounds with a standard deviation of 4.8 pounds. Construct a 95% confidence interval estimate of the difference between the mean weight losses for the two diets (assume weight loss is a normally distributed random variable). Does there appear to be a difference between the effectiveness of the two diets? Thank you for your help!

Last reply:  Tuesday, August 20, 2013 1:01 AM EST        Total Replies: 3

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