Moments of the probability density function ofR2approachedviaconditional probabilities. IV. Influence of the elimination of (low-intensity) data on the applicability ofR2in automated structure evaluation
W. K. L. Van Havere, Albert T. H. Lenstra · Acta Crystallographica Section A Foundations of Crystallography · 1983
The average value of the residual R2 and its spread σ(R2) is described as a function of a threshold a, below which Eo2 values are omitted from the data set. Theoretical expressions, valid for finite data sets in the space groups P1 and P{\bar 1}, are derived for (R2) and σ(R2) as functions of a for models containing atoms correctly as well as incorrectly positioned. Use of a threshold causes a decrease in the resolving power of R2-based strategies used in automated structure evaluations. Random elimination of Eo values gives rise to a larger loss of resolving power than does the elimination of small Eo values.