Hi Ethan,
Yes. My question was simply whether it calculates the statistics from completely unmerged intensities and just compare say h,k,l with -h,-k,l (or -h,-k,-l and h,k,-l) if there is a 2-fold? Although I believe so...
And what is a good number? Is 20 % OK? What about 30 % and even higher?
Thanks a lot,
Chen
> On May 13, 2015, at 6:07 PM, Ethan A Merritt <[log in to unmask]> wrote:
>
>> On Wednesday, 13 May, 2015 17:51:59 Chen Zhao wrote:
>> Hi all,
>>
>> I am sorry about this question which I should have figured out earlier. For
>> point group determination, does the Rmeas consider Fridel pairs
>> differently?
>
> A Friedel pair consists of the [hkl] and [-h-k-l] reflections.
> This pairing is independent of space group.
> So the agreement or lack of agreement between Friedel pairs is
> not informative about selection of point group or space group.
>
> You may be thinking of a Bijvoet pair, which consists of
> [hkl] and the Friedel mate of some symmetry equivalent of [hkl]
> within a particular spacegroup.
>
> But even in the presence of anomalous scattering I think that
> Bijvoet pairs are expected to agree with each other better than
> with a reflection not related by point group symmetry.
>
>> (although I think it should be...) This is because I saw a
>> derivative dataset collected at peak (from a demo) whose Rmeas is quite
>> high (>50 %) for all the space groups tested (including P1). However, the
>> native dataset has only <10 % Rmeas. Should I worry about the derivative
>> dataset? There seems to be multiple lattices in both datasets based on
>> IDXREF.
>>
>> You inputs are really appreciated!
>>
>> Sincerely,
>> Chen
> --
> Ethan A Merritt
> Biomolecular Structure Center, K-428 Health Sciences Bldg
> MS 357742, University of Washington, Seattle 98195-7742
>
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