Minitab Notes for Activity 4

Finding the Critical Value (Question 9)

The easiest way to find the critical values is to use your textbook. At the bottom of the z-table in the lower right hand corner of your inside front cover, there are common critical values.

However, if you would like to use Minitab to look up the critical value, you can do the following.

  1. Choose Calc / Probability Distributions / Normal
  2. Select Inverse cumulative probability
  3. The input constant is the area to the left of the critical value. Since this is a two-tail test, take one-half of the α you specified in question 11 and enter that value.
  4. Click OK

If you want the critical value on the right side, you can use the symmetry involved and just make the critical value you found above positive. Another way to find the critical value on the right directly is to repeat the steps above and use 1-α/2 for the area to the left.

Finding the Test Statistic, P-Value, and Confidence Interval (Questions 10-12)

  1. Go to Stat / Basic Statistics / 1 Proportion
  2. Click the Summarized Data radio button
  3. Enter the number of trials (n) and successes (x). Note, Minitab calls successes "events".
  4. Click Options
    1. The confidence level is the complement of the signficance level.
    2. The test proportion is the value claimed in the null hypothesis (see question 6)
    3. Check to make sure the alternative hypothesis is set correctly (see question 6)
    4. Always check the box to base the test and interval on the normal distribution (note that Minitab may complain about a small sample size, but we're not getting into non-parametric hypothesis testing at this point, so we're going to force the normal approximation).
  5. Click OK