[phenixbb] question on the missing fobs filled maps
fn1 at rice.edu
fn1 at rice.edu
Mon Nov 8 17:01:07 PST 2010
I am interesting in that at what completeness of the dataset, will one
use the missing fobs filled map for model building confidently without
too much bias included?
引用 Pavel Afonine <pafonine at lbl.gov>：
> Hi Fengyun,
>> I have two datasets, one of which the completeness is only about
>> 81%, the other one is even lower, about 45%.
>> The resulting "missing fobs filled map" is much better than the
>> unfilled map in the loop region. I read one file of Pavel on the
>> fact of maps, the concern of using missing fobs filled map is that
>> the risk of the mdoel bias.
>> My question is that could the missing fobs filled map be used for
>> the model building?
> a "missing fobs filled map" is always computed using 100% set of
> reflections. For example, if your original dataset is 81% complete,
> that means the "missing fobs filled map" is computed using existing
> 81% of data plus 19% of reflections to fill the gap. These 19% are
> DFc. In extreme case of 0% or close to 0% data completeness this
> because just Fcalc map.
> Therefore it's clear that "missing fobs filled map" map should be
> used with care, and it is a good idea to look at both maps (one
> computed using original data, and another one using the data where
> missing reflections filled in with DFc).
> "filled" maps can produce a clearer picture and may disambiguate
> hard-to-interpret density, while may be biased. Regular maps may be
> of poorer quality (due to data incompleteness), but are not model
> biased due to "filling" (although may be model biased caused by
> other reasons than "filling").
> Given data completeness you have I wouldn't use "filled" maps.
> I'm wondering what Refmac does in this case (as far as I know it
> always outputs "filled" map)?
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