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Chapter 8: Q 20. (page 508)

Losing weight Refer to Exercise 6.

a. Explain what would happen to the length of the interval if the confidence level was decreased to 90%.

b. How would a 95%confidence interval based on triple the sample size compare to the original 95%interval?

c. As Gallup indicates, the 3percentage point margin of error for this poll includes only sampling variability (what they call “sampling error”). What other potential sources of error (Gallup calls these “non sampling errors”) could affect the accuracy of the 95% confidence interval?

Short Answer

Expert verified

a. Length of interval decreases.

b. Tripling the sample size will result in narrower confidence interval than original confidence interval.

c. Under coverage bias, Selection, Non response bias.

Step by step solution

01

Given Information

Confidence interval90%,95%are given.

02

a. Effect on Length

If confidence level decreases from 95%to90%, there would be less assurance that confidence interval would have true population parameter. Confidence interval will have less values for true population parameters.

03

b. Comparison of confidence interval on tripling the sample size and original confidence interval.

Tripling sample size implies increase in sample size. It will give more details regarding population resulting in more accurate estimates. Hence, the estimate will be close to correct value and confidence interval will be narrower.

04

c. Potential Sources of Error

The errors can be:

  • Under Coverage Bias/ Selection: It exclude portion of population.
  • Response bias: It results in value different from correct value.
  • Non Response Bias: It is result of not containing data for everybody in sample.

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Most popular questions from this chapter

Can you taste PTC? PTC is a substance that has a strong bitter taste for some people and is tasteless for others. The ability to taste PTC is inherited. About 75%of Italians can taste PTC, for example. You want to estimate the proportion of Americans who have at least one Italian grandparent and who can taste PTC.

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