TDIST function

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.

How to copy an example

  1. Create a blank workbook or worksheet.

  2. Select the example in the Help topic.

    Note   Do not select the row or column headers.

    Selecting an example from Help

    Selecting an example from Help

  3. Press CTRL+C.

  4. In the worksheet, select cell A1, and press CTRL+V.

  5. 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.

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2

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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 percentage, select the cell, and then on the Sheet tab, in the Number group, click Percent Style Button image.

Applies To: Excel 2007



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