docs: function reduce() {
  		var delta = 0,
  			delta_n = 0,
  			term1 = 0;
  		/**
  		* FUNCTION: reduce( acc, data )
  		*	Defines the data reduction.
  		*
  		* @private
  		* @param {Object} acc - accumulation object containing the following properties: N, mean, M2, M3. 'N' is the observatio number. 'mean' is the mean accumulator. 'M2' is the sum of squared difference accumulator. 'M3' is the cubed difference accumulator.
  		* @param {Number} data - numeric stream data
  		* @returns {Object} accumulation object
  		*/
  		return function reduce( acc, x ) {
  			acc.N += 1;
  
  			delta = x - acc.mean;
  			delta_n = delta / acc.N;
  			
  			term1 = delta * delta_n * (acc.N-1);
  
  			acc.M3 += term1*delta_n*(acc.N-2) - 3*delta_n*acc.M2;
  			acc.M2 += term1;
  			acc.mean += delta_n;
  
  			return acc;
  		};
  	}