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: [log in to unmask] *******************************************