[3dem] [ccpem] Which resolution?

[Marin van Heel]

Hi Laurence,

One thing is certain: the 0.143 threshold is RUBBISH and all CC50 etc are
also based on the same SLOPPY STATISTICS  as are all  fixed-valued  FSC
thresholds. This controversy has been ragings for a long long time and the
errors made were extensively described (again) in our most recent paper
(Van Heel & Schatz 2017 BioRxiv:
https://www.biorxiv.org/content/10.1101/224402v1) which has been downloaded
more than 3000 times. Further papers on the issue are in the pipeline. The
math BLUNDER behind this controversy is simple:  the inner product between
a signal vector and a noise vector is NOT zero (but rather proportional to
SQRT(N) where N is the length of the vectors) and cannot be left out of the
equations. This error goes back to a paper published in Nature in 1975 and
has since been repeated frequently, including in the first paper promoting
the erroneous 0.143 FSC threshold. The consequences of this blunder in
current processing are serious especially when these erroneous metrics are
used as an optimisation criterion in iterative refinements at resolutions
close to Nyquist.  I get tired of facing this systematic misuse of the FSC
function, which I myself have introduced into the literature in 1982/1986,
and people nevertheless feel they know better (with no scientific arguments
to support!) and they feel justified to use it beyond its definition range,
and to continue to ignore the correct math. To counter this systematic
abuse of my brain child - over decades - I feel the need to use CLEAR
LANGUAGE!
Have fun!
Marin
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