Bryan, Assuming that your values of sd(I) are accurate estimates of the standard uncertainties of your Is, then I/sd(I) is a normalised variate with SU = 1. So the SU of the mean value of I/sd(I) (where as Phil says the Is are simply the measurements of the various reflections in a shell) is given by the usual formula for the SU of a mean of N variates (assumed to be statistically independent of course), i.e. 1/sqrt(N). So provided N is sufficiently large, in most cases this will be too small to worry about, e.g. for 1000 reflections per shell the uncertainty in mean(I/sd(I)) is about 0.03.
Unless I've completely got the wrong end of the stick of what you are trying to calculate, I'm not sure where the -1 and factor 2 in your formula came from (note that we are not estimating the SU of the mean from its sampling distribution, we already know the SUs of the individual measurements). HTH! -- Ian On Mon, Nov 22, 2010 at 6:33 PM, Bryan Lepore <bryanlep...@gmail.com> wrote: > [ scala 3.3.16 ] > > in scala's "final table", there's "Mean((I)/sd(I))". i could be wrong, > but the error of this measurement seems to me to exist, considering > the uncertainty of sigma = 1 / sqrt( 2 (N-1) ) ... but its not clear > where the logfile has the values of I or sigma and N that correspond > to Mean((I)/sd(I)) so i can calculate it myself. > > or, am i overlooking a table of perhaps percent data vs. I/sigma in > scala, or something else... > > -Bryan >
