Question

WEEK 5: CONFIDENCE INTERVAL CONCEPTS

Look in the newspapers, magazines, and other news sources for results of a survey or poll that show the confidence interval, usually shows as a +/- some amount. Describe the survey or poll and then describe the interval shown. How does knowing the interval, rather than just the main result, impact your view of the results?

My Responses:
Total Responses:
Number of Unread:

3
29
4

REPLY

Apr 22

13

Shelley Novick

Instead of the above question, let's start with this- Consider the formula used for any confidence interval and the elements included in that formula.

May 31

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Armen Petrosyan

Hi class, Increasing the confidence level increases the error bound, making the confidence interval wider. Decreasing the confidence level decreases

May 31

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John Goins

Hello class and Professor Novick, What happens to the confidence interval if you increase the sample size When you increase the sample size, you decr

May 31

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Rosalind McClean

Hi professor and all What happens to the confidence interval if you (a) increase the confidence level Increase the confidence level creates more room

Jun 1

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Lorraine Kremm

Good Morning Professor Jones & MATH221, The larger the sample size the the more information we have and so uncertainty reduces. Increasing the sa

Jun 1

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Lamar Waters

What happens to the confidence interval if you increase the sample size? If the sample size increases then the confidence intervals decrease as the st

Jun 1

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Jessie Jones

The confidence level will increase as the margin of error increases. If we have a random survey of 30 orange tabby's were tested on the amount of hour

Jun 1

1

Nadia Alcantara

Good Evening Professor, If we would increase the confidence level then the confidence interval becomes wider. If the sample size increase then the co

12:08 PM

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Allan Timbol

Hi Nadia, Great explanation on the math! It does have an inverse effect!

Jun 1

1

Allan Timbol

Hello Professor Novick and fellow class, In regards to sample size and margin of error, they both have an inverse relationship to one another. If one

Jun 1

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Shelley Novick

Allan, before a study is conducted the researcher determines what margin of error is acceptable. The sample size is then determined using the followi

Jun 1

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Brandy Cunha

Consider the formula used for any confidence interval and the elements included in that formula. What happens to the confidence interval if you increa

3:11 PM

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Jacqueline Juarez

Hello class, If you increase the sample size, it will decrease the width of the confidence interval. This happens because by increasing the sample siz

7:28 PM

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Cormey Reynolds

Hello Professor and class, Question: What happens to the confidence interval if you (b) increase the sample size When you increase the sample size,

May 31

2

Rosalind McClean

Hi Professor and all here's an example A political pollster plans to ask a random sample of 500 voters whether or not they support the incumbent candi

Jun 1

1

Armen Petrosyan

Hi Rosalind, You did a very good explanation and I very agree with you. Thanks for this great post for this week's discussions because your post is

10:10 PM

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Rosalind McClean

Hi Armen Thanks for the comment I like to be simple and yet clear with understanding I will try to come up with more or find more ways so that the cla

Jun 1

1

Phi Pham

Hello Class, The question of a poll could say "Are the voters going to elect Mr. Biggs or Mrs. Shine to be the mayor of the city?" Pollsters will inte

Jun 1

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Shelley Novick

Phi, using your example the confidence interval for Mrs. Shine is You would need to also calculate Mr. Biggs confidence interval to see if the two o

Jun 1

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Sharekul Islam

Hi Class Increasing the confidence level will increase the width of the confidence interval. This is due to the fact that increasing the confidence

12:26 AM

1

John Goins

Hello class and Professor Novick, An observation on how low dose aspirin does not reduce the risk death from prostate cancer. During an almost five ye

3:03 AM

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Phi Pham

Hello John, Great post for this weeks discussion. Your post has made me realize that I should stop taking more aspirin LOL

11:52 AM

4

Shelley Novick

New Question- Top of Form Class,We need to look at specific problems of confidence limits. Suppose a weight loss program like Jenny Craig or

New Question-
Top of Form
Class,
We need to look at specific problems of confidence limits. Suppose a weight loss program like Jenny Craig or Weight Watchers says that their clients lose an average of 2.6 pounds per week with a standard deviation of .3 pounds. This claim is based on a sample of 64 people from the Dallas Fort Worth area. Now we know that there are a lot more than 64 people in these programs so the population is all the people in the programs. Calculate a 99% confidence limit for the population.

How far off could this sample be from the real population? In order to answer that question we have to know 3 things. 1)What confidence level is being used 2) What is the critical ( z or t) that represents that confidence level and 3) what is the error of the sample

The formulate for our confidence interval is:
sample mean +/- Z * st dv / sq root of n

So 2.6 +/- (2.576) * (.3/(sqrt(64))
2.6 +/- (2.576) * (.3/8)
2.6 +/- .0966
2.6 - .0966 to 2.6 + .0966
2.5034 to 2.6966

You can also use the Excel template for week 5.

This means that we are 99% confident that the true population mean would fall within this confidence interval. This information may make us feel that the program is fairly reliable because the confidence interval is very "tight".

1) How would these numbers change if the sample size were 12 people?
2) How would the numbers change if the sample size were 120
people?
3) How would the numbers change if the sample size were 1200 people?

What do these answers to 1, 2 and 3 tell you about sample size?

Answer 1

Note : THe following question has been solved as the first question is unclear

Sample size = 64 and confidence interval = 99%

Sample size = 12 and confidence interval = 99%

Sample size = 120 and confidence interval = 99%

Sample size = 1200 and confidence interval = 99%

We see that as the sample size increase, the width of the confidence interval decreases.