Note: The standard deviation (SD) is a simple measure of the variablity of a data set.
It tells you how tightly all the various examples are clustered.
Smaller SD value means samples are clustered tightly, vice versa.
The median of a data set can be calculated by first sort the data set from lowest to highest (or highest to lowest), and then pick the middle value where
the lower half and the higher half have equal number of samples. If the total number of samples is even, the median then is the mean of the two sample values in the middle.
For example, the median of data set 1,2,3,4,5 is the middle value 3, which separate the lower half 1,2 from the higher half 4,5. The median of data set 1,2,3,4 is (2 + 3) / 2 = 2.5.