Re: Normally Distributed Random Number Generator from Excel
- From: Ray Vickson <RGVickson@xxxxxxx>
- Date: Fri, 28 Mar 2008 00:32:40 -0700 (PDT)
On Mar 27, 9:06 pm, "2.7182818284590..." <tangent1...@xxxxxxxxx>
wrote:
How do I create a normally distributed number with mean = 10, standard
deviation =3, and the tools that I have are:
1. =RANDBETWEEN(X, Y) - returns a uniformally-distributed number
between X to Y
2. =NORMINV(Number; Mean; STDEV)
Number represents the probability value used to determine the inverse
normal distribution.
Mean represents the mean value in the normal distribution.
STDEV represents the standard deviation of the normal distribution.
For example: =NORMDIST(70; 63; 5; 0) returns 0.03.
I would think it would be :=NORMINV(RANDBETWEEN(-2,2), 10, 3)
No! Probabilities must lie between 0 and 1, so "number" must also be
between 0 and 1.
You should be warned that several reviews have indicated the dangers
of using EXCEL for statistical computations: its algorithms are not
always good, and it may not be reliable. It sometimes delivers wrong
answers. It would be unwise to use the random number generator without
thorough testing. Microsoft has made some attempts to improve the
random number generator, but I don't think it comes up to standard
yet. I do believe that Microsoft's assurances are somewhat
overstated.
A lot depends on which version of EXCEL you are using. Some of the
problems with the statistical packages have been improved in newer
versions, while others have been, apparently, made worse. See, eg.,
http://www.stat.uiowa.edu/~jcryer/JSMTalk2001.pdf
http://www.coventry.ac.uk/ec/~nhunt/pottel.pdf
You can read the abstract of a paper on this topic at
http://portal.acm.org/citation.cfm?id=635309.635312
even if you don't have access to the full paper. Just the abstract
alone is revealing. (I can send you the file of the full paper if you
send me your e-mail address.)
R.G. Vickson
Adjunct Professor, University of Waterloo
NOTE: This is only for my interests. I'm not a student!
My goal is to create a process-simulator using MS Excel.
.
- References:
- Normally Distributed Random Number Generator from Excel
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