Minitab Notes for Activity 6

Creating the Worksheet

  1. Label the first column as mass.
  2. Enter the mass of the candy in each bag into the worksheet.

Summarizing the Sample

  1. Go to Stat / Basic Statistics / Display Descriptive Statistics
    1. Choose the mass variable
    2. Click OK

Determining Normality (may not be needed)

  1. Go to Stats / Basic Statistics / Normality Test
    1. Choose mass (C1) for the variable.
    2. Click OK
  2. Use either the normal probability plot or the Anderson-Darling p-value to determine normality.

Finding Critical Values

Minitab doesn't give critical values when it does hypothesis testing. You will need to use the degrees of freedom, level of significance, type of test, and distribution used to look up the critical value(s) from the textbook.

For those who enjoy technology, Minitab can be used to find the critical values, much like we used Excel on the third test. It uses something called the "Inverse Cumulative Probability" which takes the area in the left tail and returns the critical value for that. Note that this is different than the critical value notation, which always uses the right tail area. Here's how to find the critical value on Minitab.

  1. Go to Calc / Probability Distributions and choose the appropriate distribution
    1. Choose the "Inverse cumulative probability".
    2. Enter the degrees of freedom (if not using the normal distribution)
    3. Choose "Input Constant" and enter the area in the left tail.
      1. If you have a left tail test, just enter the area. For example, if you have 0.05 in the left tail, just enter 0.05.
      2. If you have a right tail test, you have to take 1-area to get the left tail area. For example, if you have 0.05 in the right tail, then you have 1-0.05=0.95 in the left tail. Enter 0.95 into Minitab.
      3. If you have a two-tail test, divide the area by two and repeat this exercise twice. For example, 0.05 in two tails means 0.05/2 = 0.025 in each tail. Run through this once and choose the left tail area with 0.025 and then again with a right tail area of 0.025 (follow the instructions in part ii)
    4. Click OK

Finding the Test Statistic, Probability Value, and Confidence Interval

  1. Go to Stat / Basic Statistics / 1 Sample t (or z if using normal distribution)
    1. Enter mass (C1) for the variable.
    2. Enter the claimed mass of candy for the test value.
    3. Go into Options
      1. Notice that we're doing hypothesis testing which requires a level of significance, but Minitab is asking for a confidence level instead. Make sure you enter the confidence level that agrees with our level of significance
      2. The alternative hypothesis is how you tell Minitab whether it is a left tail, right tail, or two tail test.
      3. Click OK
    4. Click OK
  2. Notice that the summary statistics are given here, so if you would have known that earlier, you could have saved some time.
  3. The confidence interval given by Minitab corresponds to the values of the mean that would fall into the non-critical region.

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Last updated March 10, 2003 10:03 PM