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ASK THE PROFESSOR FORUM

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

Ask the Professor Forum

Hi Mr. McGuckian, I have a question. Why on the example 88.5 from chapter 5.3, which asks what the smallest 5% change in waist circumference has to draw the line on the bell curve on the right (due to the fact that the people who lost more would be on the negative, and on homework question #36 the top 2% of dieters (which I assume would be the ones who had more waist reduction) are drawn in the bell curve as the line on the right? Shouldn't this problem follow the same logic than example 88.5 and the people who had more waist reduction be on the left? I am confused. Thank you for your help. Adriana Nava

Posted to STATS 1 on Thursday, March 27, 2014   Replies: 2


Professor Mcguckian
03/27/2014
3:06 PM EST

Hi Adriana,

It is because, in problem 36, they have described the loss as a positive amount. They say that they had an average decrease of 4 cm. In problem 88.5, they describe the waist change as a negative amount. They say the average was -4.69 inches. If you are on the left hand side of the curve in problem 36, you are dealing with numbers like: 1 cm, 2 cm, 3 cm, .... These amounts represent a smaller decrease. However, in example 88.5, the values on the left of the curve would be numbers like: -7 inches, -6 inches, -5 inches, .... These values would actually represent greater losses because a change of -6 inches is better than a change of only -4.69 inches. Thus, the smaller changes actually sit on the right of the mean for example 88.5.  It is all about the scale being negative.

Hopefully that makes sense,

Professor McGuckian


.
03/27/2014
4:58 PM EST
Thank You Very Much For Your Answer Professor McGuckian.

Adriana Nava

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