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StatTutor Lesson - How Confidence Intervals Behave

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      Question 1

      64

      Question 1.

      Which of the following does NOT affect margin of error?

      		A.
      		B.
      		C.
      		D.
      Incorrect. Margin of error is ME = z∗σ√n. Sample size affects margin of error as it is part of the formula; σ, the population standard deviation is also part of the formula. z* is determined by level of confidence so level of confidence affects margin of error. The value of the population, µ, is not part of the formula so it does NOT affect margin of error.
      Correct. Margin of error is ME = z∗σ√n. Sample size affects margin of error as it is part of the formula; σ, the population standard deviation is also part of the formula. z* is determined by level of confidence so level of confidence affects margin of error. The value of the population, µ, is not part of the formula so it does NOT affect margin of error.
      Incorrect. Try again.
      2

      Question 2

      181

      Question 2.

      Which of the following is the researcher unable to control?

      		A.
      		B.
      		C.
      Incorrect. Population standard deviation is what it is and no one can control it.
      Correct. Population standard deviation is what it is and no one can control it.
      Incorrect. Try again.
      2

      Questions 3-4

      250

      Question 3.

      What happens to margin of error if you increase confidence level?

      		A.
      		B.
      Incorrect. Increasing level of confidence increases z* which increases margin of error.
      Correct. Increasing level of confidence increases z* which increases margin of error.
      Incorrect. Try again.
      2

      Applet

      292

      Question 5

      336

      Question 5.

      If a researcher wants a small margin of error, what could she do?

      		A.
      		B.
      Incorrect. Increasing sample size, increases the denominator which in turn decreases margin of error. Increasing confidence level increases margin of error.
      Correct. Increasing sample size, increases the denominator which in turn decreases margin of error. Increasing confidence level increases margin of error.
      Incorrect. Try again.
      2

      Question 6

      361

      Question 6.

      True or false: If the population size is really large, then the margin of error also needs to be large.

      		A.
      		B.
      Incorrect. Population size is not part of the formula for margin of error and does not affect margin of error.
      Correct. Population size is not part of the formula for margin of error and does not affect margin of error.
      Incorrect. Try again.
      2