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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.

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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:

  1. Use a lower level of confidence:

    • The margin of error (ME) is given by the formula: ME=zσn ME = z^* \frac{\sigma}{\sqrt{n}} , where z z^* is the critical value corresponding to the desired confidence level, σ \sigma is the standard deviation, and n n is the sample size.
    • A lower level of confidence corresponds to a smaller z z^* value.
    • Therefore, using a lower level of confidence will reduce the margin of error.
  2. Increase the sample size:

    • The margin of error formula includes the term n \sqrt{n} in the denominator.
    • Increasing the sample size n n will increase n \sqrt{n} , which in turn decreases the margin of error.
    • Therefore, increasing the sample size will reduce the margin of error.
  3. Reduce σ:

    • The margin of error is directly proportional to the standard deviation σ \sigma .
    • Reducing σ \sigma will directly reduce the margin of error.
    • Therefore, reducing σ \sigma 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.

This problem has been solved

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