Am 10.01.2008 um 01:53 schrieb Dale Tronrud: ...
Your quote bring up another matter. An "initial" map, i.e. before refinement, is unbiased if it is an omit map. If you have done no refinement and you leave the interesting part out of the calculation of Fc there can not be any bias in either the Fo-Fc or the 2Fo-Fc map. This is why an initial map is more reliable for proving binding of a compound, for example, than a bias reduced map after refinement.
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But isn't this only true, if the model that is put in was not refined against a related data set before? If the new Fobs are related to the old Fobs (against which the model was refined before) then you carry any model bias over to the new data, because a simple omit-map using the old data will have model bias.
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