code: function transform( data ) {
  		var N = data.N,
  			g;
  
  		// Population skewness:
  		g = Math.sqrt( N )*data.M3 / Math.pow( data.M2, 3/2 );
  
  		// Sample skewness correction:
  		return Math.sqrt( N*N-1)*g / (N-2);
  	}
docs: end FUNCTION reduce() 
  FUNCTION: transform( data )
  Defines the data transformation.
  
  @private
  @param {Object} data - stream data
  @returns {Number} transformed data