[Ifeffit] statistical parameters

[Stefano Ciurli]

Hi Shelly,

>[Kelly, Shelly D.] Well, In my opinion that depends on where you are
>publishing the data.  If you are publishing the data in PRB then you
>should use the XX.X number.  If you are publishing in Science Magazine
>then you should use the rounded number.

clear as water :-)

>  If the answer depends on
>weather or not you round the number then I'd be suspicious.

this is not my case. I will use the XX.X number in the table. I will 
submit the paper to a biophysics type journal. I have now the 
arguments to have a dialogue with an hypothetical referee.

>Often we
>round the number so that we don't have to explain why we have a
>non-integer numbers.

clear

>You need ~ a factor of 2 for there to be a statistically significant
>difference in the reduced chi squared.  So 33.5, 30, and 40 are all
>about the same number.  Therefore I would round them all off to the
>nearest whole number that works.   I like to show changes in the reduced
>chi square rather than the absolute value.  Instead of showing a
>reduced-chi-square of 100 and 350, I show them as 1 and 3.5. Then you
>can say that 3.5 is much bigger than 1 so the model that gave 1 is the
>best.  It is the relative change in the reduced chi square that matters.

got it

>We get the absolute value wrong for a number of reasons. By showing the
>change you can side step all that explanation.

ok

>  > I know, but since I am reporting in a paper we are writing a table in
>>  which we show chi^2, reduced chi^2, Nidp and Npar (and therefore the
>>  degress of freedom) I was trying to be tidy and rigorous. But I am
>  > facing numbers which I cannot make much sense of.
>
>[Kelly, Shelly D.] That seems to be a problem.  Are you processing the
>data with more than one k-weight in IFEFFIT?

no, we use only a k^3 weight

I'll go read now Matt's mail...

Thanks
Stefano
-- 
____________________________________________

Stefano Ciurli
Professor of Chemistry
Laboratory of Bioinorganic Chemistry
Department of Agro-Environmental Science and Technology
University of Bologna
Viale Giuseppe Fanin, 40
I-40127 Bologna
Italy
Phone:	+39-051-209-6204
Fax:	+39-051-209-6203

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