[phenixbb] anisotropic induced noise amplification

James Thompson Thompson.James at mayo.edu
Wed May 2 14:06:55 PDT 2012

Anyone willing to summarize Xtriage's algorithm that determines whether "anisotropic induced noise amplification" is present in diffraction data?  What is this noise amplification?  Is it anisotropic correction factors that over-fit the data thereby inducing noise?

Many thanks,
Jim T

----------------    Anisotropy analyses     ----------------

Anisotropy    ( [MaxAnisoB-MinAnisoB]/[MaxAnisoB] ) :  3.596e-01
                          Anisotropic ratio p-value :  0.000e+00

     The p-value is a measure of the severity of anisotropy as observed in the PDB.
     The p-value of 0.000e+00 indicates that roughly 100.0 % of datasets available in the PDB have
     an anisotropy equal to or worse than this dataset.

For the resolution shell spanning between 2.36 - 2.20 Angstrom,
the mean I/sigI is equal to  3.37. 42.2 % of these intensities have
an I/sigI > 3. When sorting these intensities by their anisotropic
correction factor and analysing the I/sigI behavior for this ordered
list, we can gauge the presence of 'anisotropy induced noise amplification'
in reciprocal space.

  The quarter of Intensities *least* affected by the anisotropy correction show
    <I/sigI>                 :   3.82e+00
    Fraction of I/sigI > 3   :   5.01e-01     ( Z =     3.59 )

  The quarter of Intensities *most* affected by the anisotropy correction show
    <I/sigI>                 :   2.02e+00
    Fraction of I/sigI > 3   :   1.84e-01     ( Z =    10.78 )

The combined Z-score of    11.36 indicates that there probably is significant
systematic noise amplification that could possibly lead to artefacts in the
maps or difficulties in refinement

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