You plan to construct a confidence interval for the mean μ of a Normal population with (known) standard deviation σ. Which of the following will reduce the size of the margin of error?Use a lower level of confidence.Increase the sample size.Reduce σ.All answers are correct.
Question
You plan to construct a confidence interval for the mean μ of a Normal population with (known) standard deviation σ. Which of the following will reduce the size of the margin of error?Use a lower level of confidence.Increase the sample size.Reduce σ.All answers are correct.
Solution
To determine which actions will reduce the size of the margin of error when constructing a confidence interval for the mean μ of a Normal population with a known standard deviation σ, let's analyze each option step by step:
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Use a lower level of confidence:
- The margin of error (ME) is given by the formula: , where is the critical value corresponding to the desired confidence level, is the standard deviation, and is the sample size.
- A lower level of confidence corresponds to a smaller value.
- Therefore, using a lower level of confidence will reduce the margin of error.
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Increase the sample size:
- The margin of error formula includes the term in the denominator.
- Increasing the sample size will increase , which in turn decreases the margin of error.
- Therefore, increasing the sample size will reduce the margin of error.
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Reduce σ:
- The margin of error is directly proportional to the standard deviation .
- Reducing will directly reduce the margin of error.
- Therefore, reducing will reduce the margin of error.
Given the analysis above, all the provided options will reduce the size of the margin of error. Therefore, the correct answer is:
All answers are correct.
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