[R] Lognormal distribution - Range Factor

[Charles C. Berry]

On Sun, 1 Aug 2010, Ted.Harding at manchester.ac.uk wrote:

> On 01-Aug-10 10:59:03, Tims Corbett wrote:
>> Hi, What does it mean to say Lognormal distribution with a mean of
>> 1.03E-6 with a range factor of 100 ? How can I find the lognormal
>> distribution paramters from this information?
>>
>> Thanks, Tims
>
> If you can, please say what is meant by "range factor". I have seen
> it used to denote the ratio maximum/minimum for a sample, but it
> might be intended to mean something else in the context of your
> question.
>

Tim, you should learn to use Google to answer this question instead of 
sending postings like this to lots of differnt mailing lists.

Googling

 	lognormal "range factor"

easily turns up the definition of range factor as a function of the 
quantiles of the distribution.

FWIW, "Range factor" looks like a term of art used in certain circles.

RSiteSearch'ing (or just "??lognormal", for crying out loud!) turns up 
everything else needed to answer this, viz the R functions to find the 
quantiles, and even the relation between the mean of the lognormal and its 
parameters.

I think a little bit of algebra makes it possible to solve this directly 
from tables of the normal (or lognormal) even without having to resort to 
uniroot().

Is this homework?

HTH,

Chuck

p.s. can the posting guide advise that OT questions like this be preceeded 
by a suitable amount of Googling before coming here??


> If it does mean that, then the context is a sample of values, deemed
> to be log-normally distributed, with (presumably) the sample mean
> equal to 1.03E-6 (0.00000103) and max/min=100. However this would
> be really inadequate information to determine what the parameters
> of the log-normal distribution might be. At the very least one needs
> also the sample size, and even then the determination would not be
> reliable.
>
> Ted.
>
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> Date: 01-Aug-10                                       Time: 12:33:45
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Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901