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

ID: Q173923

The information in this article applies to:

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)

where X is the numeric value at which to evaluate the distribution. For example, the following formula

   =TDIST(-1.96,60,2)

returns a #NUM! error because the X argument is negative.

This behavior is by design of Microsoft Excel.

RESOLUTION

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

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.

The "Function Reference" and Help files do not mention any restrictions for the X argument. However, the following additional information applies:

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

Additional query words: XL98 XL97 XL7 XL5 XL4

Keywords          : xlformula xlhelp 
Version           : MACINTOSH:4.0,5.0,5.0a,98; WINDOWS:4.0,4.0a,5.0,5.0c,7.0,7.0a,97
Platform          : MACINTOSH WINDOWS
Issue type        : kbprb

Last Reviewed: January 8, 1999