The Excel BETADIST Function

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Related Functions:

BETAINV

BETADIST and BETA.DIST

In Excel 2010, the Betadist function has been replaced by the Beta.Dist function, which has improved accuracy.

Although it has been replaced, the Betadist function is still available in Excel 2010 (stored in the list of compatibility functions), to allow compatibility with earlier versions of Excel.

Basic Description

The Excel BETADIST function calculates the cumulative beta probability density function for a supplied set of parameters.

The format of the function is :

BETADIST( x, alpha, beta, [A], [B] )

Where the function arguments are:

x	-	The value at which the function is to be calculated (must be between [A] and [B])
alpha	-	A parameter of the distribution (must be > 0)
beta	-	A parameter of the distribution (must be > 0)
[A]	-	An optional argument which gives the lower bound of the interval of x (if omitted, [A] takes the default value 0)
[B]	-	An optional argument which gives the upper bound of the interval of x (if omitted, [B] takes the default value 1)

If the arguments [A] and [B] are set to 0 and 1 respectively, the function calculates the Standard Cumulative Beta Distribution.

Betadist Function Example

The chart on the right shows the Standard Cumulative Beta Distribution with the parameter alpha set to 4 and the parameter beta set to 5.

If you want to use Excel to calculate the value of this function at x = 0.4, this can be done with the Betadist function, as follows:

=BETADIST( 0.4, 4, 5 )

This gives the result 0.4059136.

Note that, in the above function call, the arguments [A] and [B] have been omitted, and so take on the default values 0 and 1 respectively. This is the Standard Cumulative Beta Distribution.

Plot of Standard Cumulative Beta Distribution with Alpha=4 and Beta=5

Standard Cumulative Beta Distribution Function with α = 4 and β = 5

Further information and examples of the Excel Betadist function can be found on the Microsoft Office website.

Trouble Shooting

If you get an error from the Excel Betadist function this is likely to be one of the following :

Common Errors

#NUM!

Occurs if either:

-	the supplied x value is < [A] or > [B]
or
-	the supplied [A] and [B] arguments are equal
or
-	the supplied alpha or the supplied beta argument is ≤ 0

#VALUE!

Occurs if any of the supplied arguments are non-numeric

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