Documentation/Calc Functions/TDIST

TDIST

Category:

Statistical Analysis

Summary:

Calculates area to the tail(s) of the probability density function of the Student's t-distribution(often known more simply as just the t-distribution). The Student's t-distribution is often used to test a hypothesis about a population’s mean when the population’s standard deviation is not known. The Student’s t-distribution can be used with any statistic whose distribution is approximately normal.

Syntax:

TDIST(Number; DegreesFreedom; Mode)

Returns:

Returns a positive real number in the range 0 to 1 (exclusive) representing the total area under the tail(s) of the probability distribution function of the specified Student’s t-distribution.

Arguments:

Number is a non-negative real number or a reference to a cell containing that number which is the value for the Student's t-distribution is to be calculated.

DegreesFreedom is a positive integer value or a reference to the cell containing that number which is the number of degrees of freedom for the Student's t-distribution.

Mode = 1 returns the one-tailed test, Mode = 2 returns the two-tailed test.

• If Number is less than 0 then the function returns an error value.
• If DegreesFreedom is less than 1 then the function returns an error value.
• If DegreesFreedom and Mode is a non-integer value then the function uses its floor value, i.e. it is truncated to an integer.
• If Mode is less than 1 or greater than or equal to 3 then the function returns an error value.

• The formula for TDIST is:

where

Here, x is the Number, df is DegreesFreedom and tails is Mode.

• It is such that T.DIST.RT(x ,y) = 0.5*T.DIST.2T(x, y), T.DIST.RT(x, y) = TDIST(x, y, 1), T.DIST.RT(x, y) = 1 – T.DIST(x, y, 1) and T.DIST.2T(x, y) = TDIST(x, y, 2).
• For more details about the Student's t-distribution, visit Wikipedia.

Examples:

Formula Description Returns
=TDIST(5.8;1.5;1) The function calculates the area to the single-tailed probability density function of the Student’s t-distribution. Here DegreesFreedom is non-integer value 1.5 so the function truncates it to integer 1. 0.054346705732263
=TDIST(5.8;1.5;2) The function calculates the area to the two-tailed probability density function of the Student’s t-distribution. Here DegreesFreedom is non-integer value 1.5 so the function truncates it to integer 1. 0.108693411464525
=TDIST(5.8;1.5;3) The function returns an error value since Mode can only be 1 or 2. Err:502

TDIST