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~~== what do R-factors try to measure, and how to interpret their values? ==~~
−~~* relative deviation of~~
−~~=== Data quality ===~~
−~~* typical values: ...~~
−~~=== Model quality ===~~
−

To my knowledge, the only program that implements this currently (December 2008) is [[xds:XDSSTAT|XDSSTAT]].

To my knowledge, the only program that implements this currently (December 2008) is [[xds:XDSSTAT|XDSSTAT]].

+
+=== Comparing two sets of structure factor amplitudes or intensities ===

+The following is symmetric, and suitable for comparing two data sets, or two model amplitudes:

+<math>

+ R=\frac{\sum_{hkl}\vert F_{hkl}^{i}-F_{hkl}^{j}\vert}{\sum_{hkl} 1/2 (F_{hkl}^{i}+F_{hkl}^{j})}

+</math>

+for amplitudes, and analogously for intensities:

=== Model quality indicators ===

=== Model quality indicators ===

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<br>

<br>

where <math>F_{hkl}^{obs}</math> and <math>F_{hkl}^{calc}</math> have to be scaled w.r.t. each other. R and R<sub>free</sub> differ in the set of reflections they are calculated from: R is calculated for the [[working set]], whereas R<sub>free</sub> is calculated for the [[test set]].

where <math>F_{hkl}^{obs}</math> and <math>F_{hkl}^{calc}</math> have to be scaled w.r.t. each other. R and R<sub>free</sub> differ in the set of reflections they are calculated from: R is calculated for the [[working set]], whereas R<sub>free</sub> is calculated for the [[test set]].

−==== Relation between R and R<sub>free</sub> as a function of resolution ====

==== Relation between R and R<sub>free</sub> as a function of resolution ====

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