**Definition:**

Average figure of merit of phases of reflections included in the refinement. This value is derived from the likelihood function FOM = I_1(X)/I_0(X) I_0, I_1 = zero- and first-order modified Bessel functions of the first kind X = sigma_A |E_o| |E_c|/SIGMA E_o, E_c = normalized observed and calculated structure factors sigma_A = <cos 2 pi s delta_x> SQRT(Sigma_P/Sigma_N) estimated using maximum likelihood Sigma_P = sum_{atoms in model} f^2 Sigma_N = sum_{atoms in crystal} f^2 f = form factor of atoms delta_x = expected error SIGMA = (sigma_{E;exp})^2 + epsilon [1-(sigma_A)^2] sigma_{E;exp} = uncertainties of normalized observed structure factors epsilon = multiplicity of diffracting plane Ref: Murshudov, G. N., Vagin, A. A. & Dodson, E. J. (1997). Acta Cryst. D53, 240-255.

**Type:** float

**Mandatory item:** no

**Category:** refine

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