# Two Sample t-Test Assuming Unequal Variances

## You can do t-Test in Excel using the Analysis Toolpak, but...

• Excel won't interpret your p-value for you; the QI Macros will!
• Excel can't give you a Box and Whisker chart of the two factors; the QI Macros can!

How do you determine if the variances are equal or unequal? Use an F-test to determine if the variances are equal or unequal.
If they are equal go to: Two-Sample t-Test assuming equal variances.
(The QI Macros Stat Wizard will do this for you automatically.)

### Example of a Two Sample t-Test Assuming Unequal Variances

In this example, we want to compare two types of structural steel and want to know if the strengths (in 1000 lbs/sq. in.) are the same or different. Next we conduct some tests and enter the data into Excel:

Warning: While you can run a t-Test using Excel's Data Analysis Toolpak, if you don't enter the two columns in the correct order, Excel statistics will give you incorrect results. The QI Macros have eliminated this problem.

### How to Perform a t-Test Assuming Unequal Variances using QI Macros for Excel

1. Select the data with the mouse and click on the QI Macros Menu, Statistical Tools and then t-Test two sample assuming unequal variances:

2. The QI Macros will prompt for a significance level (default is .05):

3. Next the QI Macros will prompt for the hypothesized difference in the means (default is 0).

If you specify a mean difference other than zero, use:
• two-tail p value (Difference = Hypothesized Mean Difference)
• one-tail p value (Difference < Hypothesized Mean Difference)
• 1-one tail p value (Difference > Hypothesized Mean Difference)

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The QI Macros will perform the calculations and interpret the results for you:

### What's Unique About t-Test Calculations in the QI Macros?

When you run the t-test in Excel, the QI Macros will compare the p-value (0.197) to the significance level (0.05) and interpret the results for you. Cannot Reject the Null Hypothesis because p > 0.05" and that the "Means are the same".