Global indicators of X-ray data quality

Global indicators of the quality of diffraction data are presented and discussed, and are evaluated in terms of their performance with respect to various tasks. Based on the results obtained, it is suggested that some of the conventional indicators still in use in the crystallographic community should be abandoned, such as the nominal resolution d(min) or the merging R factor R-merge, and replaced by more objective and more meaningful numbers, such as the effective optical resolution d(eff,opt) and the redundancy-independent merging R factor R-r.i.m.. Furthermore, it is recommended that the precision-indicating merging R factor R-p.i.m. should be reported with every diffraction data set published, because it describes the precision of the averaged measurements, which are the quantities normally used in crystallography as observables.