Refinement . Refinement of F 2 against ALL reflections. The weighted R -factor wR and goodness of fit S are based on F 2 , conventional R -factors R are based on F , with F set to zero for negative F 2 . The threshold expression of F 2 > σ ( F 2 ) is used only for calculating R -factors(gt) etc . and is not relevant to the choice of reflections for refinement. R -factors based on F 2 are statistically about twice as large as those based on F , and R - factors based on ALL data will be even larger.