Oh, I thought the sigmas were derived from the differences in intensities of the multiple measurements of a given reflection--I guess both the individual-measurement counting stats and differences in measurements must be combined in the end. But, what does the software do if somehow a sigma=0 creeps in, or more generally, what is the best statistical approach for this?
JPK On Thu, Aug 23, 2012 at 12:44 PM, Jim Pflugrath <jim.pflugr...@rigaku.com>wrote: > Singly-measured reflections should have a sigma from Poisson counting > statistics, so that should not be a problem. A problem might occur if the > X-ray background is exactly zero and the observed (sic) intensity is > exactly zero. > > > ------------------------------ > *From:* CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Jacob > Keller [j-kell...@fsm.northwestern.edu] > *Sent:* Thursday, August 23, 2012 12:36 PM > *To:* CCP4BB@JISCMAIL.AC.UK > *Subject:* [ccp4bb] Calculating I/sig when sig = 0 > > Dear Crystallographers, > > what approach is taken to calculate I/sig when sig = 0? (This could > happen for singly-measured reflections or perhaps some other scenario, such > as rejection of other measurements leaving only one measurement.) I could > imagine alternatives, but what is actually done? > > 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 *******************************************
