There seems to be an epidemic of papers with I/Sigma > 3 (sometime much
larger). In fact such cases have become so frequent that I fear some
people start to believe that this is the proper procedure. I don't know
where that has come from as the I/Sigma ~ 2 criterion has been
established long ago and many consider that even a tad conservative. It
simply pains me to see people going to the most advanced synchrotrons to
boost their highest resolution data and then simply throw away much of it.
I don't know what has caused this wave of high I/Sigma threshold use but
here are some ideas
- High I/Sigma cutoffs are normal for (S/M)AD data sets where a more
strict focus on data quality is needed.
Perhaps some people have started to think this is the norm.
- For some dataset Rsym goes up strongly while I/SigI is still
reasonable. I personally believe this is due to radiation damage which
affects Rsym (which compares reflections taken after different amounts
of exposure) much more than I/SigI which is based on individual
reflections. A good test would be to see if processing only the first
half of the dataset improves Rsym (or better Rrim)
- Most detectors are square and if the detector is too far from the
crystal then the highest resolution data falls beyond the edges of the
detector. In this case one could, and should, still process data into
the corners of the detector. Data completeness at higher resolution may
suffer but each additional reflection still represents an extra
restraint in refinement and a Fourier term in the map. Due to crystal
symmetry the effect on completeness may even be less than expected.
Bart
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
roberto.battistu...@unipd.it
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
============================================================================
