Using an adaptive measure of spread throughout.  The scale factor
reported for a bandwidth can appear to be small when the standard
deviation is inflated due to the presence of outliers.  Furthermore,
supplying a scale factor of, say, 1.06 for density estimation when
there are outliers that inflate the standard deviation may oversmooth
rather dramatically in the presence of outliers.  We now use the
measure found in Silverman (1986, equation (3.30)) which is
min(standard deviation, interquartile range/1.349). This robust choice
produces expected results in the presence of outliers.