Minitab Instructions for Chapter 5 Technology Exercise

Minitab ALWAYS returns the area to the left of a z-value.

Finding Areas (Question 1)

This uses the cumulative probability distribution, which is the area to the left of the z-score.

  1. Choose Calc / Probability Distributions / Normal
  2. Make sure Cumulative Probability is checked
  3. Check Input constant and enter your z-score in the box
  4. Click OK

The value that Minitab returns will be the area to the left. To find the area to the right, subtract the area to the left from one.

The "twice smaller value" is found by taking the smaller of the two areas and multiplying it by two. Why we do this will become more apparent in later chapters.

Finding Z-Scores (Question 2)

This uses the inverse cumulative probability, which gives you the z-score when you know the area to the left.

  1. Choose Calc / Probability Distributions / Normal
  2. Make sure Inverse Cumulative Probability is checked
  3. Check the input constant radio button
    1. If the area you know is the area to the left, enter it into the box
    2. If the area you know is the area to the right, subtract it from one and then enter it into the box
    3. If the area is some other area, you have to figure out how much is to the left and then enter that into the box.
  4. Click OK

ACT Test Scores (Question 3)

This question is like questions 1 and 2 except we are no longer working with a standard normal distribution.

Pick the appropriate set of instructions from above, but change the mean and the standard deviation to the appropriate values before continuing.

Sampling Distributions (Question 4)

You don't need Minitab or Statdisk for this question. Go to the statistical demonstrations page and choose the Sampling Distribution from section 5.5.

Confidence Interval Simulations (Question 5)

You don't need Minitab or Statdisk for this question. Go to the statistical demonstrations page and choose the Confidence Interval Simulation from section 6.2.

Be sure you explain how the confidence level relates to the process of finding a confidence interval.

Direction of Country (Question 6)

Read the Harris Poll® #16, February 16, 2006, at http://www.harrisinteractive.com/harris_poll/index.asp?PID=640

  1. Choose Stats / Basic Statistics / 1 Proportion
  2. You have the summarized data
  3. The number of trials is the sample size, n, for the survey that you found for part b.
  4. The number of events is the number of successes, x, which represents the number of people who feel that the country is seriously off on the wrong track. This is NOT the percent of people that you found for part a, but you'll have to take that percent of the total sample size and round it to a whole number to enter here.
  5. Click on Options
    1. Make sure the confidence level is set correctly
    2. Ignore the test proportion (we'll use this in chapter 7)
    3. Check the box that says "use test and interval based on normal distribution"
  6. Click OK

The confidence interval will be given in parentheses under the heading "95% CI". You should write it in inequality notation; for example, if Minitab says (0.46234, 0.56725), then you should write 0.46234 < p < 0.56725.