On Wed, 2010-04-21 at 17:21 -0700, James Holton wrote: > The "0.3% chance" of a peak being above 3 > "sigmas" assumes that the histogram of electron density values is > Gaussian. It is not! In fact, it is a funny-looking bimodal > distribution (the peaks are protein and solvent regions).
Indeed! That's why it is a "bizarre" argument. In fact, standard deviation is rather meaningless unless one is dealing with "univariate" distribution. For bimodal distributions, changes of standard deviation are uninterpretable (without looking at the distribution, that is) since they can be due to both shifts and redistribution. Cheers, Ed. -- Edwin Pozharski, PhD, Assistant Professor University of Maryland, Baltimore ---------------------------------------------- When the Way is forgotten duty and justice appear; Then knowledge and wisdom are born along with hypocrisy. When harmonious relationships dissolve then respect and devotion arise; When a nation falls to chaos then loyalty and patriotism are born. ------------------------------ / Lao Tse /
