Hello Joerg, > -Having measured n counts, the estimated value is n+1
You might have a hard time convincing me on that one. > -Having measured n counts, the esd is also sqrt(n+1)! If n is zero then spending more time on the data collection might be better than more time on the analysis. > Things change with variable counting times. id31sum uses counts=counts and esd=sqrt(counts+alp) where alp=0.5 is the default and can be overridden on the command line. Perhaps there aren't many people who use that option. Should we change the default? The 0.5 came from the literature but it was some time ago and I can't remember where. In any case it then gets convoluted with the monitor error. Sqrt(n+1) gives a very low chi^2 if the actual background is 0.1 (eg: 1 count every 10 datapoints). Might be better to just use the Poisson itself, as in abfit [1]. > the above correction for the estimated > values gave significant better R values. Are you using background subtracted R-values? If only R-values were significant. Jon [1] Acta Cryst. (1990). A46, 692-711 Maximum-likelihood methods in powder diffraction refinements A. Antoniadis, J. Berruyer and A. Filhol ------------------------------------------------- This mail sent through IMP: http://horde.org/imp/
