As has been shown recently (and discussed on this board), Rsym is not the
best measure of data quality (if any measure at all):
http://www.sciencemag.org/content/336/6084/1030.abstract
> narayan viswam wrote:
>> Hello CCP4ers,
>>
In my data, the highest reolution shell 2.8-3.0 A has I/sigmaI 2.5
&
>> Rsym 224.3 %
>> for multiplicity 7.8 and
completeness 98.2 %. I solved the structure by
>> MAD &
refined it
>> to Rfree 27.3 %. Ths crystal belongs to P622
space group and it is not
>> twinned. The water
>>
content is 68%. I loweredthe multiplicity to 4.1 by excluding few
>> images but still the
>> Rsym is > 200 % and
I/sigmaI > 2.0. My rudimentary crystallography
>> knowledge
makes me
>> believe it's quite Ok to use data upto 2.8 A and
report the statistics.
>> Could I request
>>
people's views. Thanks very much.
>> Narayan
>
> After refinement, what is R-free in the last shell? If it is
significantly
> better
> than random, say around .4 or
less, that could be taken as evidence that
> there
> is
data in the last shell.
> Also check the error model- Rsym >2
sort of implies the error is greater
> than
> the signal,
so I/sigI 2 seems surprising.
> eab
>
--
Edwin Pozharski, PhD
University of Maryland, Baltimore
