Minitab Notes for Activity 9

The following examples assume the brands of paper towels are "bounty", "northern", "brawny", and "scott". Adjust the instructions to fit your data if necessary.

Entering the Data into Minitab

1. Label one column as "brand" and another column as "diameter"
2. Choose Calc / Make Patterned Data / Text Values
   1. Store the patterned data into the brand column
   2. The text values should be: bounty northern brawny scott. If any of your brands have a space in them, then you would need to enclose that particular brand in quotes, for example: bounty northern "brawny super" scott
   3. List each value 5 times (if you have six drops for each, then list each value 6 times).
   4. Click OK
3. Enter the diameters for each observation into the diameter column

Generating the One-Way Analysis of Variance (Question 3)

1. Choose Stat / ANOVA / One-Way
2. The response variable is diameter
3. The factor is brand
4. Click OK

Use the results of the ANOVA table to answer questions 4 and 5.

Finding the Critical F value (Question 6)

There are three options available in Minitab for dealing with probability distributions.

• Probability density - This option returns the probability density function for a specific value. The probability density function corresponds to the height of the curve at a specific value, so this would be useful for making a graph of the distribution.
• Cumulative probability - This option returns the area to the left of a critical value or test statistic. This would be useful for finding a p-value when you know the test statistic.
• Inverse cumulative probability - This option returns the critical value or test statistic that has the given area to the left. This would be useful for finding a critical value from the significance level.

Okay, so of those options, the inverse cumulative probability is the one we need to use.

1. Choose Calc / Probability Distributions / F
2. Select Inverse Cumulative Probability.
3. Leave the non-centrality parameter at 0, we're not in graduate school.
4. Enter the correct degrees of freedom. The numerator df is the df for the factor (one less than the number of brands) and the denominator df is the df for the error (within) source (total sample size minus number of factors).
5. Click on Input Constant. The inverse cumulative probability gives the number with the inputted area to the left of it, but this is a right tail test. That means we need to subtract the signficance level from one and enter that as the constant.
6. Click OK.

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Last updated May 4, 2007 3:03 AM