Distribution of the 10-cluster radii associated with the average absolute difference in VTEC for 2011 deviates significantly from a normal distribution. The solid gray bars correspond to the empirical distribution of data. The three smooth curves represent three different attempts to approximate the empirical distribution by normal distributions with parameters derived by three different algorithms: standard (blue), robust algorithm (red) where data points far away from median are removed, and off-centered normal (black) where the median is replaced by the highest point of the empirical distribution in the rejection of outliers.