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research papers
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, 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.