_Normdist ( z ; mu ; sigma )
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Mislav Kos, Soliant Consulting
http://www.soliantconsulting.com
FileMaker implementation of NORMDIST Excel function
Sample Input:
( 100; 100; 15 )
( 90 ; 100; 15 )
( 70 ; 100; 15 )
( 130; 100; 15 ) 

Sample Output:
0.500000001
0.252492467
0.022750062
0.977249938
Compare to Excel
0.500000000
0.252492538
0.022750132
0.977249868 

Description:
PURPOSE:
To provide a near equivalent of the NORMDIST Excel function, for when its "cumulative" parameter is set to true.
RESULT:
The cumulative probability that the observed value of a normal random variable with mean mu and standard deviation sigma will be less than or equal to parameter z.
DEPENDENCIES:
This custom function requires the _Normsdist ( z ) custom function.
NOTES:
This custom function is a FileMaker implementation of the NORMDIST function in Excel.
Caution: This custom function is ONLY AN APPROXIMATION of the Excel function;
i.e. it will calculate an approximate answer rather than the exact answer.
(Note: The same is true of the Excel function.)
The results are accurate to several decimal places, which is typically sufficient for most uses.
Also see the custom function _Normsdist ( z ).
The difference between NORMDIST and NORMSDIST:
 NORMSDIST applies to standard normal distribution.
 NORMDIST applies to any normal distribution.
 A standard normal distribution has a mean of 0 and a standard deviation of 1.
The calculation was adapted from http://www.wilmott.com/messageview.cfm?catid=8&threadid=78622.
Here are some notes on the NORMDIST Excel function from http://support.microsoft.com/kb/827371:
 The normal distribution is a continuous probability distribution whose shape is determined by its mean, mu, and standard deviation, sigma.
 The normal distribution with mean mu and standard deviation sigma is centered at mu and has half of its probability to the left of mu and half to the right.
 The /standard/ normal distribution is the special case where mu = 0 and sigma = 1.
 The probability is distributed according to the familiar bellshaped curve with the total area under the curve equal to 1.
 The probability that a value that is less than or equal to z will occur (also called cumulative probability up to z) is the area under this curve to the left of z.
 In NORMDIST, when the last argument is set to TRUE, NORMDIST returns the cumulative probability that the observed value of a Normal random variable with mean mu and standard deviation sigma will be less than or equal to z.
Note: these functions are not guaranteed
or supported by BrianDunning.com. Please contact the individual
developer with any questions or problems.
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