t-Test Assuming Unequal Variance Returns Incorrect DF Value

• Microsoft Excel for Windows, versions 4.0, 4.0a

SYMPTOMS

In Microsoft Excel, when you use the Analysis ToolPak t-Test: Two-Sample Assuming Unequal Variances function or tool, the degree of freedom (df) that is returned is incorrect.

Degree of freedom should be a whole number. The two-sample assuming unequal variances returns a decimal (real) number.

STATUS

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. This problem has been corrected in Microsoft Excel version 5.0.

MORE INFORMATION

The t-Test: Two-Sample Assuming Unequal Variances tool performs a two-sample student's t-test. This form of the test assumes that the variances of both ranges of data are unequal and is referred to as a heteroscedastic t-test.

When to use a t-test

Use a t-test to determine whether two sample means are equal. Use this test when the groups under study are distinct. Use a paired test when there is one group before and after a treatment.