But it is highly unlikely that sum(I) in the denominator is zero if I/sig(I) is 2 as reported (providing the sig(I) is 
valid- what was chi^2 in the last shell and overall?).

I sort of disagree that R-merge values over 1.0 are meaningless, provided not too far over. Granted R-meas is more 
meaningful, but with high redundancy R-merge approximates R-meas, and R-merge is what the PDB is accepting now.  A value 
a little over 1 tells you the standard deviation of the individual mesurements is a little larger than the average 
signal in those measurements. Understanding a little about distribution of intensities and error propogation (standard 
error of the mean, R-pim) the user will understand that quite a few reflections were stronger than this standard 
deviation, and that the error in the averaged intensities is be less than this standard deviation, and not have a 
problem. The problem comes with the "100%-sum" mentality which says that if your error is 100% the signal must be zero%. 
That is why I don't like to express R-whatever as a percent. If the signal was really zero, R-merge or R-meas would be 
plus/minus infinity. So much for 100%-sum.

So rerun scalepack with "no merge original index", reprocess through CCp4 or just rune Diedrich's "rmerge" program or 
phenix.merging_statistics to get the value of r-merge (and r-meas and R-pim and cc1/2) from the .sca file. If it is much 
over 3 than I would rexamine the I/sig(I) value (which "can be misestimated") and consider discarding the last shell. If 
it is 3 or less, report it. The PDB ADDIT2 application used to not accept values over .99, but you can put that and ask 
the friendly annotator to correct it in the final PDB file. If the annotator objects, THEN point (him) to the 2012 K&D 
paper- R-meas in the last shell there was over 4, and they concluded there was useful information.

Of course by then you will have refined your structure, and unbiased R-free in the last shell can be a good indicator. 
If you refine once in phenix you can use phenix.cc_star to calculate cc* and compare with R and R-free; from the output 
mtz file and your unmerged .sca file.
eab

Frank von Delft wrote:
> This HKL2000 (scalepack) feature is actually extremely sensible:  an Rmerge that high is mathematically meaningless, it
> quite literally tells you nothing at all about he signal in your data.
>
> So I second James's advice:  just put "n/a" in your table 1.
>
> If the reviewer complains, point them to Karplus & Diederichs, Science, 2012, and Evans and Murshudov, ActaD, 2013, and
> tell them to join us in the 21st century.
>
>
>
>
> On 14/08/2013 16:41, Jeffrey, Philip D. wrote:
>> Hello Yafang,
>>
>> The answer lies in the fact that you used HKL2000.  Scalepack has a long standing "feature" where it reports Rmerge >
>> 100% as zero.  Quite why they do that is a mystery, but your Rmerge in the outermost shell is NOT zero - the Rmerge
>> for the lower resolution shells will show up as non-zero if Rmerge < 100%.
>>
>> That feature is overdue for a fix.
>>
>> Alternatively export your scaled data with NO MERGE ORIGINAL INDEX and import into CCP4 via Pointless and have Scala
>> or Aimless report the correct statistics.  Reprocessing the data using XDS or Mosflm will ultimately lead you to
>> scaling the data with a program that doesn't have that bug.  If you do this, report Rmeas rather than Rmerge, the
>> former being a better measure.
>>
>> Phil Jeffrey
>> Princeton
>>
>>
>> ------------------------------------------------------------------------------------------------------------------------
>> *From:* CCP4 bulletin board [[log in to unmask]] on behalf of Yafang Chen [[log in to unmask]]
>> *Sent:* Wednesday, August 14, 2013 11:32 AM
>> *To:* [log in to unmask]
>> *Subject:* Re: [ccp4bb] Rmerge of the last shell is zero
>>
>> Dear All,
>>
>> Here are some more details about the question I asked earlier about "Rmerge is 0 in the last shell". I processed the
>> data using HKL2000. The space group is I213. Redundancy is 10.2 (10.3). I/sigma is 34.8 (2.3). Rmerge is 6.5 (0.0).
>> Since I/sigmaI is more than 2 in the last shell, I preferred not to cut back the resolution any more. But I don't know
>> how to explain Rmerge in the last shell being 0. Besides, I am wondering if this data is publishable (with Rmerge
>> being 0 in the last shell). Thank you so much for your help!
>>
>> Best,
>> Yafang
>>
>>
>> On Wed, Aug 14, 2013 at 10:59 AM, Yafang Chen <[log in to unmask] <mailto:[log in to unmask]>> wrote:
>>
>>     Dear All,
>>
>>     I recently processed a dataset, in which I/sigmaI of the last shell is 2.3, while Rmerge of the last shell is 0.
>>     Does anyone know why the Rmerge is 0? The completeness is 100 (100). Thank you so much for your help in advance!
>>
>>     Best,
>>     Yafang
>>
>>     --
>>     Yafang Chen
>>     Graduate Research Assistant
>>     Mesecar Lab
>>     Department of Biological Sciences
>>     Purdue University
>>     Hockmeyer Hall of Structural Biology
>>     240 S. Martin Jischke Drive
>>     West Lafayette, IN 47907
>>
>>
>>
>>
>> --
>> Yafang Chen
>> Graduate Research Assistant
>> Mesecar Lab
>> Department of Biological Sciences
>> Purdue University
>> Hockmeyer Hall of Structural Biology
>> 240 S. Martin Jischke Drive
>> West Lafayette, IN 47907
>