XL: TDIST Function Returns #NUM! If X Argument Is Negative

• Microsoft Excel 98 Macintosh Edition
• Microsoft Excel 97 for Windows
• Microsoft Excel for Windows 95, versions 7.0, 7.0a
• Microsoft Excel for Windows, versions 4.0, 4.0a, 5.0, 5.0c
• Microsoft Excel for Windows NT, version 5.0
• Microsoft Excel for the Macintosh, versions 4.0, 5.0, 5.0a

SYMPTOMS

In Microsoft Excel, if you enter a formula that uses the TDIST function, the formula may return a #NUM! error. This behavior may occur even when you use a value greater than or equal to 1 for the Degrees_Freedom argument and a value of 1 or 2 for the Tails argument.

CAUSE

This behavior occurs if the X argument is negative (less than zero) in the following syntax

   TDIST(x,degrees_freedom,tails)

   =TDIST(-1.96,60,2)

RESOLUTION

To resolve this problem, use a value that is greater than or equal to zero for the X argument in the TDIST function.

STATUS

This behavior is by design of Microsoft Excel.

MORE INFORMATION

In Microsoft Excel, the TDIST function allows you to calculate the Student's t-distribution. The t-distribution is used in the hypothesis testing of small sample data sets. You can use the TDIST function in place of a table of critical values for the t-distribution.

The "Function Reference" for Microsoft Excel 4.x and the Microsoft Excel Help file for other versions of Microsoft Excel include the following information about the TDIST function:

• If any argument is nonnumeric, the TDIST function returns a #VALUE! error.
• The Degrees_Freedom and Tails arguments are truncated to integers.
• If Degrees_Freedom is less than 1, the TDIST function returns a #NUM! error.
• If Tails has a value other than 1 or 2, the TDIST function returns a #NUM! error.

   If X is less than 0, the TDIST function returns a #NUM! error.