IMPROVED FIGURES OF MERIT FOR DIRECT METHODS

The figures of merit (FOMs) proposed in a recent paper [Cascarano, Giacovazzo & Viterbo (1987). Acta Cryst. A43, 22-29] are modified to improve their efficiency. It is shown that FOMs based on psi-zero triplets and FOMs based on the distribution of the concentration parameter alpha can be treated by the same mathematical formalism. An earlier FOM, the R(Karle) criterion, is revised and suggestions are given for its efficient use. The use of the correlation coefficient is also suggested, provided large- and small-intensity reflections are used simultaneously.