**Definition:**

The correlation coefficient between the observed and calculated structure factors for reflections not included in the refinement (free reflections). The correlation coefficient is scale-independent and gives an idea of the quality of the refined model. sum~i~(Fo~i~ Fc~i~ - <Fo><Fc>) R~corr~ = ------------------------------------------------------------ SQRT{sum~i~(Fo~i~)^2^-<Fo>^2^} SQRT{sum~i~(Fc~i~)^2^-<Fc>^2^} Fo = observed structure factors Fc = calculated structure factors <> denotes average value summation is over reflections not included in the refinement (free reflections)

**Type:** float

**Mandatory item:** no

**Category:** refine

Copyright © 2005 International Union of Crystallography