The `GAMMADIST` function in Excel is used to return the gamma distribution, which is commonly used in statistics to model the times to failure for various processes. The function can be implemented in Excel as follows:
Syntax:
GAMMADIST(x, alpha, beta, cumulative)
Parameters:
- x: The value at which the gamma distribution is evaluated. It must be a non-negative number.
- alpha: The shape parameter of the distribution, often referred to as “a” or “k”. It must be a positive number.
- beta: The scale parameter of the distribution, often referred to as “b” or “θ”. It also must be a positive number.
- cumulative: A logical value that determines the form of the function. If `TRUE`, `GAMMADIST` returns the cumulative distribution function; if `FALSE`, it returns the probability density function.
Example:
Suppose you want to calculate the cumulative gamma distribution for a value ( x = 2 ), with an alpha value of 3 and a beta value of 2.
=GAMMADIST(2, 3, 2, TRUE)
- Enter the following formula in an Excel cell:
This will return the cumulative distribution value.
=GAMMADIST(2, 3, 2, FALSE)
- If you want the probability density function instead, use:
Additional Notes:
- The shape and scale parameters need to be greater than 0 for the function to work properly.
- In newer versions of Excel (Excel 2010 onwards), a similar function called `GAMMA.DIST` is available that accepts the same arguments and offers backward compatibility with `GAMMADIST`.
By using the `GAMMADIST` function, you can model various processes or datasets by adjusting the alpha and beta parameters to fit the specific curve of your data distribution.
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