The default sigma cutoff (in denzo) is -3 and I wouldn't override that
without good reason. The cut-off is applied before averaging equivalent
reflections (but after adding partials?). If you reject all negative
observations of a particular reflection and average the remaining
positive observations, you will get an artificially inflated estimate
of the intensity.
Even if the intensity is negative after averaging, the French&Wilson
treatment in truncate will give you a positive F in the end.
Apparently there is some information in the negative reflections,
i.e. the most likely value of Fobs for a reflection with Iobs= -0.01 sigma
is greater than that for a reflection with Iobs=-1.5 sigma.
Ed
protein.chemist protein.chemist wrote:
What is the Sigma Cutoff that one should use for Data Processing using
HKL2000.
Is there a minimum or maximum value.
Also if there is a variation then what all does it depend on.
Thanks in Advance for your help.
Mariah
--
Mariah Jones
Department of Biochemistry
University of Florida
