Moments of the probability density function of R₂ approached via conditional probabilities. V. Incorporation of the a priori knowledge of atomic coordinates in the evaluation of moments of R₂

First and second moments of P(R₂) are evaluated for models denoted symbolically by {g, f; a}, containing a atoms known a priori to be correct, g (new) atoms correctly and f (new) atoms incorrectly placed. Formulas are derived, valid for the space groups P1 and P, using explicitly the set of observed reflections as well as the a priori knowledge about the a atoms. It is demonstrated that the implementation of the latter information decreases σ(R₂) and enhances considerably the resolving power of R₂-based criteria to discriminate between a correct and an incorrect model.