Proposition: what the paper below describes (map variance) would be
rather useful to access routinely (e.g. in coot etc), given that it
describes how to calculate by FFT.
Discuss. (No, I've not read any of it carefully.)
/Acta Cryst./ (2012). A*68*, 464-469 [ doi:10.1107/S0108767312015772 ]
A practical study of the electron-density-map variance
C. Giacovazzo and A. Mazzone
An algorithm is described for the calculation of the variance of the
electron density /via/ fast Fourier transform. The main features of the
ratio /electron density/standard deviation/ are described; it is shown
that such a ratio may be considered a useful criterion for estimating,
on an absolute scale, the quality of an electron-density map, no matter
the quality of the model and the data resolution. In some way, it is a
good estimate of the confidence one should have in the reliability of
the proposed structure. The ratio was tested both for observed and for
difference Fourier syntheses, in order to control the usefulness of the
criterion for the most popular maps in crystallography.
