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Documentation/Calc Functions/T.DIST

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Function name:

T.DIST

Category:

Statistical Analysis

Summary:

Calculates t-distribution values from either the probability density function or the cumulative distribution function. The t-distribution is often known as the Student's t-distribution.

T-distributions are a family of continuous probability distributions and each has a curve with the same general bell shape that is symmetric about 0. Each t-distribution is characterized by a parameter known as the number of degrees of freedom, often denoted by the lowercase Greek letter nu ([math]\displaystyle{ \nu }[/math]). The t-distribution approaches the normal distribution as the number of degrees of freedom increases. T-distributions are often used to model small sample sizes.

Syntax:

T.DIST(Number; Degrees freedom; Cumulative)

Returns:

Returns a non-negative real number, which is the t-distribution value for the given arguments. For the probability density function, the value returned lies in the range [0, 0.4]. For the cumulative distribution function, the value returned lies in the range [0, 1].

Arguments:

Number is a real number, or a reference to a cell containing that number, which is the value at which the t-distribution is to be evaluated.

Degrees freedom is a positive integer, or a reference to a cell containing that number, which is the number of degrees of freedom of the t-distribution. This is typically assumed to be the number of samples minus 1.

Cumulative is a logical value, or a reference to a cell containing that value, that determines whether the required probability is taken from the probability density function or the cumulative distribution function. If Cumulative is set to 0 or FALSE, a value from the probability density function is calculated. For any other values of Cumulative a value from the cumulative distribution function is calculated.

  • If any of Number, Degrees freedom, or Cumulative is non-numeric, then T.DIST reports a #VALUE! error.
  • If Degrees freedom is less than 1, then T.DIST reports an invalid argument error (Err:502).
  • If Degrees freedom is a non-integer value, then T.DIST truncates it to an integer value.

Additional details:

  • T.DIST is provided for interoperability with Microsoft Excel.
  • Calc provides four related functions that return values from the t-distribution and these are:
  • T.DIST. Calculates t-distribution values from either the probability density function or the cumulative distribution function of the specified t-distribution. These are sometimes referred to as "left tailed" values.
  • T.DIST.2T. Calculates the total area under the two tails of the probability density function of the specified t-distribution. This represents the total probability that the value of a random variable lies below [math]\displaystyle{ -\text{ABS}(Number) }[/math] or above [math]\displaystyle{ +\text{ABS}(Number) }[/math].
  • T.DIST.RT. Calculates the total area under the right tail of the probability density function of the specified t-distribution. This represents the total probability that the value of a random variable lies above Number.
  • TDIST. A dual purpose function that can calculate either of the two types of value calculated by T.DIST.2T or T.DIST.RT.
  • The formula for the probability density function of the t-distribution is:
[math]\displaystyle{ PDF_t(x;\:\nu)~=~\frac{ \Gamma\!\left(\frac{\nu +1}{2}\right)}{\sqrt{\pi\:\nu}~~\Gamma\!\left(\frac{\nu}{2}\right)}\left (1+\frac{x^2}{\nu}\right)^{ -\frac{(\nu+1)}{2}} }[/math]
where
  • [math]\displaystyle{ \Gamma }[/math] is the gamma function.
  • [math]\displaystyle{ \nu }[/math] is the (positive) number of degrees of freedom of the t-distribution.
Note that the random variable x in the above formula often appears as t in other sources.
  • The formula for the cumulative distribution function of the t-distribution is:
[math]\displaystyle{ CDF_t(x;\:\nu)~=~\int_{-\infty}^{x}\frac{ \Gamma\!\left(\frac{\nu +1}{2}\right)}{\sqrt{\pi\:\nu}~~\Gamma\!\left(\frac{\nu}{2}\right)}\left (1+\frac{t^2}{\nu}\right)^{ -\frac{(\nu+1)}{2}} dt }[/math]
  • The following figure shows probability density function plots for four sample t-distributions.
  • The following figure shows cumulative distribution function plots for four sample t-distributions.
  • The name space for T.DIST is COM.MICROSOFT.T.DIST.
  • For more information on the t-distribution, visit Wikipedia's Student's t-distribution page.

Examples:

Formula Description Returns
=T.DIST(A1; A2; A3) where cells A1:A3 contain the values 0.5, 2, and 0 respectively. Here the function calculates a value from the probability density function of the t-distribution. Note that the formula =T.DIST(0.5; 2.9; FALSE) returns the same value because the Degrees freedom argument is truncated to an integer value. 0.296296296296296
=T.DIST(0.5; 2; TRUE) Here the function calculates a value from the cumulative distribution function of the t-distribution. 0.666666666666667
=T.DIST(0; 25; 0) Here the function calculates the peak value from the probability density function of the t-distribution with 25 degrees of freedom. 0.394973789636461

Related LibreOffice functions:

T.DIST.2T

T.DIST.RT

T.INV

T.INV.2T

TDIST

TINV

ODF standard:

None

Related (or similar) Excel functions:

T.DIST since v.2010.