higher redundancy lowers Rpim because it increases precision. However,
it need not increase accuracy if the observations are not drawn from the
"true distribution". If pathologic behaviour of Rfactor statistics is
due to radiation damage, as I believe is often the case, we are
combining observations that are no longer equivalent. If you used long
exposures per image and collected just enough data for a complete data
set you are out of luck. If you used shorter exposures and opted for a
high-redundancy set then you have the option to toss out the last N
images to get rid of the most damaged data, or you can try to compensate
for the damage with zerodose, or whatever the name was of the program, I
think from Wolfgang Kabsch.
Rejecting data is never desirable but I think it may be better than
merging non-equivalent data that can't be properly modeled by a single
structure.
Bart
On 11-03-03 12:34 PM, Bernhard Rupp (Hofkristallrat a.D.) wrote:
>> I don't like Rmeas either.
> Given the Angst caused by actually useful redundancy, would it not be more
> reasonable then to report Rpim which decreases with redundancy? Maybe Rpim
> in an additional column would help to reduce the Angst?
>
> BR
>
> Maia
>
> Tim Gruene wrote:
>> Hello Maia,
>>
>> Rmerge is obsolete, so the reviewers had a good point to make you
>> publish Rmeas instead. Rmeas should replace Rmerge in my opinion.
>>
>> The data statistics you sent show a mulltiplicity of about 20! Did you
>> check your data for radiation damage? That might explain why your
>> Rmeas is so utterly high while your I/sigI is still above 2 (You
>> should not cut your data but include
>> more!)
>>
>> What do the statistics look like if you process just about enough
>> frames so that you get a reasonable mulltiplicity, 3-4, say?
>>
>> Cheers, Tim
>>
>> On Thu, Mar 03, 2011 at 10:57:37AM -0700, Maia Cherney wrote:
>>
>>> I see, there is no consensus about my data. Some people say 2.4A,
>>> other say all. Well, I chose 2.3 A. My rule was to be a little bit
>>> below Rmerg 100%. At 2.3A Rmerg was 98.7% Actually, I have published
>>> my paper in JMB. Yes, reviewers did not like that and even made me
>>> give Rrim and Rpim etc.
>>>
>>> Maia
>>>
>>>
>>>
>>> Bernhard Rupp (Hofkristallrat a.D.) wrote:
>>>
>>>> First of all I would ask a XDS expert for that because I don't know
>>>> exactly what stats the XDS program reports (shame on me, ok) nor
>>>> what the quality of your error model is, or what you want to use the
>>>> data for (I guess refinement - see Eleanor's response for that, and use
> all data).
>>>> There is one point I'd like to make re cutoff: If one gets greedy
>>>> and collects too much noise in high resolution shells (like way
>>>> below<I/sigI> =
>>>> 0.8 or so) the scaling/integration may suffer from an overabundance
>>>> of nonsense data, and here I believe it makes sense to select a
>>>> higher cutoff (like what exactly?) and reprocess the data. Maybe one
>>>> of our data collection specialist should comment on that.
>>>>
>>>> BR
>>>>
>>>> -----Original Message-----
>>>> From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf
>>>> Of Maia Cherney
>>>> Sent: Thursday, March 03, 2011 9:13 AM
>>>> To: [log in to unmask]
>>>> Subject: Re: [ccp4bb] I/sigmaI of>3.0 rule
>>>>
>>>> I have to resend my statistics.
>>>>
>>>> Maia Cherney wrote:
>>>>
>>>>> Dear Bernhard
>>>>>
>>>>> I am wondering where I should cut my data off. Here is the
>>>>> statistics from XDS processing.
>>>>>
>>>>> Maia
>>>>>
>>>>>
>>>>>> On 11-03-03 04:29 AM, Roberto Battistutta wrote:
>>>>>>
>>>>>>> Dear all,
>>>>>>> I got a reviewer comment that indicate the "need to refine the
>>>>>>> structures
>>>>>>>
>>>>>> at an appropriate resolution (I/sigmaI of>3.0), and re-submit the
>>>>>> revised coordinate files to the PDB for validation.". In the
>>>>>> manuscript I present some crystal structures determined by
>>>>>> molecular replacement using the same protein in a different space
>>>>>> group as search model. Does anyone know the origin or the
>>>>>> theoretical basis of this "I/sigmaI>3.0" rule for an appropriate
>>>>>> resolution?
>>>>>>
>>>>>>> Thanks,
>>>>>>> Bye,
>>>>>>> Roberto.
>>>>>>>
>>>>>>>
>>>>>>> Roberto Battistutta
>>>>>>> Associate Professor
>>>>>>> Department of Chemistry
>>>>>>> University of Padua
>>>>>>> via Marzolo 1, 35131 Padova - ITALY tel. +39.049.8275265/67 fax.
>>>>>>> +39.049.8275239 [log in to unmask]
>>>>>>> www.chimica.unipd.it/roberto.battistutta/
>>>>>>> VIMM (Venetian Institute of Molecular Medicine) via Orus 2,
>>>>>>> 35129 Padova - ITALY tel. +39.049.7923236 fax
>>>>>>> +39.049.7923250 www.vimm.it
>>>>>>>
>>>>>>>
>>>>
>>
--
===========================================================================
Bart Hazes (Associate Professor)
Dept. of Medical Microbiology& Immunology
University of Alberta
1-15 Medical Sciences Building
Edmonton, Alberta
Canada, T6G 2H7
phone: 1-780-492-0042
fax: 1-780-492-7521
===========================================================================
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