Re: [ccp4bb]: A simple question of resolution

[Jim Pflugrath <jwp@RigakuMSC.com>]

***  For details on how to be removed from this list visit the  ***
***          CCP4 home page http://www.ccp4.ac.uk         ***

We define in our structural biology contracts that the maximum resolution
is where the average I/sigmaI for the high resolution shell is 2 for all
possible reflections in the shell.  Please note the use of the word
average.  

Furthermore, the average I/sigI is calculated before averaging
redundancies.  That is, the calculation is made on the input reflections
and not on the averaged unique reflections that are output and used in
subsequent calculations.  The average I/sigI for the output averaged
reflections will be a function of the input unaveraged I/sigI and the
redundancy (i.e. multiplicity) of the input reflns.

There is not much reason to have completeness less than 99%
nowadays.  So if you have <I/sigI> of 2, but only 50% completeness, that's
really <I/sigI> of just 1.  

We have found that some programs do not report the proper I/sigI.  Maybe
I can get Tassos to comment on this.

Jim