Two-Sample t-Test in Excel

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

  • Excel's interface can be confusing; QI Macros adds a new tab to Excel's menu making t tests point and click simple
  • Excel won't interpret your p-value for you; QI Macros Add-in will!
  • Excel can't give you a Box and Whisker chart of the two factors; QI Macros Add-in can!

Two-Sample t test Example

Lets say you're producing rubber made from two different recipes and you want to know if the tensile strengths are the same or different. You test five samples of each to get the data:

Next Determine if the Variances are Equal or Unequal

In order to select the correct Two Sample t test, you need to determine if the variances are equal or unequal. QI Macros offers two options:

  • Use the QI Macros Stat Wizard. It will run an f test and then automatically choose the right t test for you.
  • Run an F-test on the data to determine if the variances are equal or unequal. Then run the t test.

To Run the t-test Using QI Macros

  1. Select the data and click on the QI Macros Menu -> Statistical Tools-> t test: Two-Sample Assuming Equal Variances or Unequal Variances depending on the f test results:
  2. t test two sample equal variances in the QI Macros

  3. QI Macros will prompt you for a significance level:

    two sample t test significance level
    Note: Significance Level = (1 - Confidence Level).

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

  5. QI Macros will perform the calculations and interpret the results for you:
t test two sample calculation in QI Macros

QI Macros compares the p-value (0.818) to the significance level (0.05) and tells you "Cannot Reject the Null Hypothesis because p>0.05 (Means are the same)."

QI Macros also draws a Box Plot to help you visualize the difference between the variances (height of box and length of whiskers) and means (line of box where the color changes.)

Tip: 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)


Watch This Video to See QI Macros Run a t -test


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