Re: [ccp4bb] poll: cutoff for "high resolution"

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From: "Meyer, Peter" pameyer {- at -} MCW {- dot -} EDU
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Subject: Re: poll: cutoff for "high resolution"
From: James Holton JMHolton {- at -} LBL {- dot -} GOV
Date: 2008-05-16

IMHO the word "high" is an useless way to describe your resolution.
We're scientists. We measure things. Things called numbers. So why
not use them?

The words "high" and "low" are about as useful in scientific literature
as "large" and "small", "many" and "few", "old" and "new" or the
ever-popular "several". I always hate it when I ask my users how big
their crystals are and they tell me they are "really small". A "small"
crystal in 1988 was 300 um on a side. What is a small crystal now? How
about 20 years from now? These things depend on a context that changes
over time. There was once a time when 5A was "high resolution" for
myoglobin (1955). What is worse about resolution in particular is that
the colloquial "high" corresponds to smaller numbers! This DOES confuse
people!

I'm not saying the words should be banned, but if you are going to use
them, you really ought to put it in context. Preferably using Angsroems
or at least an SI unit.

As for what resolution is "high" (where higher resolution corresponds to
smaller d-spacings), you can always look to the PDB for statistics. If
you make a histogram of PDB entries vs the "REMARK 2" resolution, then
you get a slightly lopsided Gaussian distribution centered at 2.0 A with
a width of 1.1 A:
http://bl831.als.lbl.gov/~jamesh/pickup/resolution_historgram.png

This probably has a lot more to do with the psychology of
crystallographers and editors than any kind of physical phenomenon in
the crystals. Note the sharp rise crossing over 2.0 A. But if you want
to say your resolution is "higher than average", then 2.0 A seems to
qualify as the cut-off. If you want to say it is really high, then it
is perhaps useful to know that only 10% of the PDB is better than 1.6A
and a different 10% is worse than 2.8 A.

-James Holton
MAD Scientist

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CCP4bb <-- 2008 <-- May 2008 <-- 16 May 2008

Previous message:
Subject: Re: Phaser compile errors
From: "Meyer, Peter" pameyer {- at -} MCW {- dot -} EDU
Date: 2008-05-16

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From: Raja Dey deyraja1 {- at -} YAHOO {- dot -} CO {- dot -} IN
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