Dear colleagues, this is a request for comments on the evaluation of crystal structures that resulted from twin refinement.
>From http://www.ysbl.york.ac.uk/~garib/refmac/Tutorials/refmac_tutorial.pdf: "Although Rfactors are substantially smaller with twin refinement than without twin refinement it does not mean that model also is substantially better. [...] Usually twin maps after twin refinement are more biased towards errors in the model." >From phenix.xtriage output: "Please note however that R-factors from twinned refinement cannot be directly compared to R-factors without twinning, as they will always be lower when a twin law is used. You should also use caution when interpreting the maps from refinement, as they will have significantly more model bias." How would you ascertain that inclusion of twin parameters has improved the model? How is one to judge the evidentiary strength of such crystal structure in general, given that validation by residuals and maps is further weakened compared to refinement without twinning parameters? Thank you for your thoughts and time, Wolfram Tempel
