   - parameter values: Array of decimal numbers.
   - returns: The median value from the array. Returns nil for an empty array. Returns the greater of the two middle values if there is an even number of items in the array.
 
-  Example
+  Example:
 
       Sigma.medianHigh([1, 12, 19.5, 10, 3, -5]) // 10
    


  σx is the population standard deviation of x.

  Example

      let x = [1, 2, 3.5, 3.7, 8, 12]
      let y = [0.5, 1, 2.1, 3.4, 3.4, 4]


  n is the sample size.

  Example:

      Sigma.standardDeviationSample([1, 12, 19.5, -5, 3, 8]) // 8.674195447801869

