statistical calculation

Frank Koormann frank.koormann at
Thu Apr 17 07:05:35 CEST 2008


Am Mittwoch, 16. April 2008 16:51:51 schrieb vincent.gregorio at
> I have questions about the statistical calculation on great-er. In the
> pre-processing step, i don't understand if is it the mean flow or the
> median flow to enter in the .rna file( i have a lognormal distibution of
> flow values)?

The flow statistics are assumed to be lognormal distributed. The commonly 
available descriptive parameters are mean flow and percentiles, hence 
GREAT-ER requires the Q_mean and the Q_5.

> What is the q_stdev calculate( does great-er transform the 
> lognormal distribution in a normal distribution? ) 

The upload transforms the descriptive parameters of the lognormal 
distribution, since internally it is easier to derive MC-Shots from a 
(Mean, StdDev) distribution description.

> and how does great-er 
> make monte-carlo simulation (results of concentration are given in
> percentile, but is it for a lognormal or normal distribution?)

GREAT-ER generates series of random numbers depending on the given standard 
distribution of a parameter (constant, uniform, normal or lognormal) which 
are then transformed into the actual distribution of the parameter. 
The results are considered as lognormal distributed (GREAT-ER desktop Manual, 
section "Calculate River Csim X")
> is it possible to have more information about that?

Hope this helps.



Frank Koormann  |  ++49-541-335 08 30  |
Intevation GmbH, Georgstr. 4, 49074 Osnabrück, DE | AG Osnabrück, HR B 18998
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