Minitab Notes for Activity 8

Entering the Data (Question 4)

Label an empty column of the worksheet as "mass"
Enter the masses that you collected in question 4 in that column.

Summarize the Sample (Question 6)

Choose Stat / Basic Statistics / Display Descriptive Statistics
Select the mass variable
Click OK.

Checking Normality (Question 9)

Generate a graphical summary of the data

Choose Stat / Basic Statistics / Graphical Summary
Select the mass variable
Click OK.

The only thing you can't tell from that is the question about the probability plot although it might be easier to spot outliers on the probability plot than the histogram (depending on how far out there they are). To generate a probability plot, do the following.

Choose Stat / Basic Statistics / Normality Test (or you can choose Graph / Probability Plot / Single)
Select the mass variable
Click OK

Finding the Critical Values (Question 17)

The easiest way to find the critical values is to go to Table T in your appendix and look up the value(s). If you are using a normal distribution (see question 15), then use the bottom row of the t-table where it says infinity.

However, if you want to do this with Minitab, you can do the following. These instructions assume you're using a t distribution. If you're using a normal distribution, then choose normal in step 1 instead of t and ignore the part about degrees of freedom.

Choose Calc / Probability Distributions / t
Check Inverse Cumulative Probability
Enter the proper degrees of freedom
Click the Input Constant radio button
Enter the area to the left of the critical value into the Input Constant box. Minitab always takes the area to the left, so you'll have to adjust if you're not working with a left tail already.
1. If you have a left tail test, this is alpha. For example, if your significance level was 0.10, then you would enter 0.10 into the box.
2. If you have a right tail test, this is 1-alpha. For example, if your significance level was 0.10, then you would enter 0.90 into the box.
3. If you have a two tail test, then you need to repeat this whole process two times. The first time, use alpha/2 for the area on the left and 1-alpha/2 for the area on the right. For example, if your significance level was 0.10, then there would be half of that (0.05) on each side. The first time through, you would use 0.05 and the second time through you would use 0.95.
Click OK

Finding the Test Statistic, p-value, and confidence interval (Questions 20-22)

The place to go in Minitab depends on whether you said your test statistic had a normal or t distribution in step 15. In either case, only do one of the following.

Student's T Distribution - Sample Standard Deviation known

Go to Stat / Basic Statistics / 1-Sample t
Select mass as your variable to test
Enter the claimed mean in the "test mean" box
Go into options
1. The confidence interval should agree with your significance level. If your significance level is 0.10 (10%), then your confidence level should be 90%.
2. Make sure the alternative hypothesis is set properly for your problem.
3. Click OK
Click OK

Notice how the summary statistics are given. You didn't have to do a separate step in question 6 to find them, they're given here. However, we wanted to check for normality, so it was a good thing we did question 6.

Normal Distribution - Population standard deviation known

Go to Stat / Basic Statistics / 1-Sample z
Select mass as your variable to test
Enter the population standard deviation into the sigma box. If you don't have the population standard deviation, you shouldn't be using the normal test.
Enter the claimed mean in the "test mean" box
Go into options
1. The confidence interval should agree with your significance level. If your significance level is 0.10 (10%), then your confidence level should be 90%.
2. Make sure the alternative hypothesis is set properly for your problem.
3. Click OK
Click OK

Changing to a One-Tail Test (Question 28)

Repeat the section above for questions 20-22, but under options, change the alternative to be a greater than.
Click OK