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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.
How to copy an example

• 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.

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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 .
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