Hi Jacob, I think a lot of people do use I/sigma :o)
However sigma is in some cases poorly defined, and the merging residuals you refer to are calculated only from the I values and are related to I/sigma anyhow... Of course the R values are sometimes also poorly defined for low multiplicity data. Best wishes, Graeme On 27 January 2012 17:55, Jacob Keller <j-kell...@fsm.northwestern.edu> wrote: > Clarification: I did not mean I/sigma of 2 per se, I just meant > I/sigma is more directly a measure of signal than R values. > > JPK > > On Fri, Jan 27, 2012 at 11:47 AM, Jacob Keller > <j-kell...@fsm.northwestern.edu> wrote: >> Dear Crystallographers, >> >> I cannot think why any of the various flavors of Rmerge/meas/pim >> should be used as a data cutoff and not simply I/sigma--can somebody >> make a good argument or point me to a good reference? My thinking is >> that signal:noise of >2 is definitely still signal, no matter what the >> R values are. Am I wrong? I was thinking also possibly the R value >> cutoff was a historical accident/expedient from when one tried to >> limit the amount of data in the face of limited computational >> power--true? So perhaps now, when the computers are so much more >> powerful, we have the luxury of including more weak data? >> >> JPK >> >> >> -- >> ******************************************* >> Jacob Pearson Keller >> Northwestern University >> Medical Scientist Training Program >> email: j-kell...@northwestern.edu >> ******************************************* > > > > -- > ******************************************* > Jacob Pearson Keller > Northwestern University > Medical Scientist Training Program > email: j-kell...@northwestern.edu > *******************************************
