Free R: Difference between revisions
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[[Free R]] (also called R<sub>free</sub>) "is generally considered the most useful global measure of model-to-data agreement"<ref name="validation4pdb">PMID: 22000512</ref>. It is a statistical quantity introduced in 1992 by Axel T. Brünger<ref name="bruenger">PMID: 18481394</ref> to assess the quality of a model from X-ray crystallographic data. It is calculated in the same manner as the [[R value]], but from a subset of the data set aside for the calculation of free R, and not used in the refinement of the model. It is a more reliable tool for assessing the model than the R value because it is not self-referential -- that is, as an estimation of errors, free R is free of any bias that may have been introduced during refinement. Free R is an example of the application of the more general method of [http://en.wikipedia.org/wiki/Cross-validation_(statistics) cross validation]. | [[Free R]] (also called R<sub>free</sub>) "is generally considered the most useful global measure of model-to-data agreement"<ref name="validation4pdb">PMID: 22000512</ref>. It is a statistical quantity introduced in 1992 by Axel T. Brünger<ref name="bruenger">PMID: 18481394</ref> to assess the quality of a model from X-ray crystallographic data. It is calculated in the same manner as the [[R value]], but from a subset of the data set aside for the calculation of free R, and not used in the refinement of the model. It is a more reliable tool for assessing the model than the R value because it is not self-referential -- that is, as an estimation of errors, free R is free of any bias that may have been introduced during refinement. Free R is an example of the application of the more general method of [http://en.wikipedia.org/wiki/Cross-validation_(statistics) cross validation]. | ||
==Help Interpreting Free R== | |||
When a crystallographic protein structure is visualized in [[FirstGlance/Index|FirstGlance in Jmol]], its Free R will be automatically interpreted as ''Reliability'' with the following levels, each relative to its [[Resolution]]: | |||
*<span style="color:#00e000;font-weight:bold;">Much better than average</span> | |||
*<span style="color:green;font-weight:bold;">Better than average</span> | |||
*<span style="color:black;font-weight:bold;">Average</span> | |||
*<span style="color:#a0a000;font-weight:bold;">Worse than average</span> | |||
*<span style="color:red;font-weight:bold;">Unreliable</span> | |||
==Good Values for Free R== | ==Good Values for Free R== | ||
