STATISTICAL DESCRIPTORS IN CRYSTALLOGRAPHY .2. REPORT OF A WORKING GROUP ON EXPRESSION OF UNCERTAINTY IN MEASUREMENT

The Working Group has examined recent recommendations for evaluating a nd expressing uncertainty in measurement [Guide to the Expression of U ncertainty in Measurement, International Organization for Standardizat ion (ISO, 1993)]. The present publication updates an earlier report of the IUCr Subcommittee on Statistical Descriptors [Schwarzenbach, Abra hams, Flack, Gonschorek, Hahn, Huml, Marsh, Prince, Robertson, Rollett & Wilson (1989). Acta Cryst. A45, 63-75]. This new report presents th e concepts of standard uncertainty, of combined standard uncertainty, and of Type A and Type B evaluations of standard uncertainties. It exp ands the earlier dictionary of statistical terms, recommends replaceme nt of the term estimated standard deviation (e.s.d.) by standard uncer tainty (s.u.) or by combined standard uncertainty (c.s.u.) in statemen ts of the statistical uncertainties of data and results, and requests a complete description of the experimental and computational procedure s used to obtain all results submitted to IUCr publications.