# TDIST

Returns the Percentage Points (probability) for the Student t-distribution where a numeric value (x) is a calculated value of t for which the Percentage Points are to be computed. The t-distribution is used in the hypothesis testing of small sample data sets. Use this function in place of a table of critical values for the t-distribution.

Syntax

TDIST(x,degrees_freedom,tails)

X     is the numeric value at which to evaluate the distribution.

Degrees_freedom     is an integer indicating the number of degrees of freedom.

Tails     specifies the number of distribution tails to return. If tails = 1, TDIST returns the one-tailed distribution. If tails = 2, TDIST returns the two-tailed distribution.

Remarks

• If any argument is nonnumeric, TDIST returns the #VALUE! error value.
• If degrees_freedom < 1, TDIST returns the #NUM! error value.
• The degrees_freedom and tails arguments are truncated to integers.
• If tails is any value other than 1 or 2, TDIST returns the #NUM! error value.
• If x < 0, then TDIST returns the #NUM! error value.
• If tails = 1, TDIST is calculated as TDIST = P( X>x ), where X is a random variable that follows the t-distribution. If tails = 2, TDIST is calculated as TDIST = P(|X| > x) = P(X > x or X < -x).
• Since x < 0 is not allowed, to use TDIST when x < 0, note that TDIST(-x,df,1) = 1 – TDIST(x,df,1) = P(X > -x) and TDIST(-x,df,2) = TDIST(x df,2) = P(|X| > x).

Example

The example may be easier to understand if you copy it to a blank worksheet.

• Create a blank workbook or worksheet.
• Select the example in the Help topic.

Note   Do not select the row or column headers.

Selecting an example from Help
• Press CTRL+C.
• In the worksheet, select cell A1, and press CTRL+V.
• To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.
A B
Data Description
1.959999998 Value at which to evaluate the distribution
60 Degrees of freedom
Formula Description (Result)
=TDIST(A2,A3,2) Two-tailed distribution (0.054644927, or 5.46 percent)
=TDIST(A2,A3,1) One-tailed distribution (0.027322464 or 2.73 percent)

Note   To view the number as a percent, select the cell and, on the Format menu, click Cells. Click the Number tab, and then click Percentage in the Category box.

Applies to:
Excel 2003