A simple (not for me) question !

how can I compute the mean and standard deviation of a weibull
distribution in excel ?

I need this because I'd like to find which alpha and beta gives a
weibull distribution with a specific mean and variance; so I was
thinking of using the solver and therefore I need a way to compute the
mean and variance given alpha and betas ...

Thanks in advance

Paolo


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kayard
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Hi Paolo,

This link might help you,

http://www.qualitydigest.com/jan99/html/weibull.html

Regards,
Bondi

Bondi referenced a nice article for working with Weibull data, but the OP's
question of calculating moments from parameters is not answered there. For
that question, refer to
http://mathworld.wolfram.com/WeibullDistribution.html
In Excel, the mean of the Weibull(alpha,beta) distribution is given by
=beta*EXP(GAMMALN(1+1/alpha))
and the standard deviation is given by
=beta*SQRT(EXP(GAMMALN(1+2/alpha))-EXP(GAMMALN(1+1/alpha))^2)

Excel's GAMMALN is not very accurate for arguments very near 1 or 2 (<1
though that is irrelevant here), with the result that the standard deviation
calculation becomes increasingly inaccurate for alpha500.

Jerry

"kayard" wrote:


A simple (not for me) question !

how can I compute the mean and standard deviation of a weibull
distribution in excel ?

I need this because I'd like to find which alpha and beta gives a
weibull distribution with a specific mean and variance; so I was
thinking of using the solver and therefore I need a way to compute the
mean and variance given alpha and betas ...

Thanks in advance

Paolo


--
kayard
------------------------------------------------------------------------
kayard's Profile: http://www.excelforum.com/member.php...o&userid=24716
View this thread: http://www.excelforum.com/showthread...hreadid=532893