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I think is is just a matter of convenience when changing resolution limits and trying to use the same test set. If you always want 1000 but your next crystal doesn't diffract as well you have to select a few more reflections and they will have been in the working set previously. If the next crystal diffracts better you have to convert some of your old test set to working set so you can add some high res reflections to the test set. If you stick with percents life is simpler. The cost, of course is that you often have more than 1000 reflections in the test set which, while giving you a more reliable free R, cause a larger degradation in the model itself. Dale Tronrud On 11/20/2014 2:43 PM, Keller, Jacob wrote: > Dear Crystallographers, > > I thought that for reliable values for Rfree, one needs only to > satisfy counting statistics, and therefore using at most a couple > thousand reflections should always be sufficient. Almost always, > however, some seemingly-arbitrary percentage of reflections is > used, say 5%. Is there any rationale for using a percentage rather > than some absolute number like 1000? > > All the best, > > Jacob > > ******************************************* Jacob Pearson Keller, > PhD Looger Lab/HHMI Janelia Research Campus 19700 Helix Dr, > Ashburn, VA 20147 email: kell...@janelia.hhmi.org > ******************************************* > -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (MingW32) iEYEARECAAYFAlRudacACgkQU5C0gGfAG13bNgCcCKISpiajkA8NbI+hzsuHdC1O RaoAniJDw+hWuHuxkqGVF+qkWOHkynqi =IH/N -----END PGP SIGNATURE-----
