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Re: [ccp4bb]: Contour
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> I would suggest that your hypothetical example is not of any relevance
> to macromecular crystallography. There are ALWAYS errors in a model,
> even in the final stages of refinement, because there is never
> sufficent data to be able to model all aspects of conformational
> mobility/disorder. A 5 sigma peak in an Fo-Fc difference map, even
> close to the "end" of refinement, can be interpreted with very high
> confidence as indicating an error in the model. As I mentioned
> earlier, in many cases it may not be possible to interpret these
> features, but this does not mean they have no significance.
so you suggest that we should go back to the dark
ages and put a water in every 3 sigma Fo-Fc peak ?
(that's what people may be tempted to do after
reading this)
and again: "5 sigma" is a meaningless concept in an
Fo-Fc map - you must talk in absolute terms. we're
talking about electrons here, not statistics. saying
that 'N sigma' is a significant feature no matter what
is like saying that a beer should cost one currency
unit in every country, i.e. a pound in the uk and a
lira in italy. you need to put them on an absolute
scale (e.g., euros ;-)
--gerard
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Gerard J. Kleywegt
[Research Fellow of the Royal Swedish Academy of Sciences]
Dept. of Cell & Molecular Biology University of Uppsala
Biomedical Centre Box 596
SE-751 24 Uppsala SWEDEN
http://xray.bmc.uu.se/gerard/ mailto:gerard@xray.bmc.uu.se
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