code: function quartiles( data ) {
  		var qValues = new Array( 2 ),
  			vector;
  
  		vector = new Array( data.length );
  		for ( var i = 0; i < data.length; i++ ) {
  			vector[ i ] = data[ i ][ 1 ];
  		}
  
  		qValues[ 0 ] = quantile( vector, 0.25 );
  		qValues[ 1 ] = quantile( vector, 0.75 );
  		
  		return qValues;
  	}
docs: end FUNCTION ascending() 
  FUNCTION: quartiles( data )
  Computes quartiles for a dataset array.
  
  @private
  @param {array} data - sorted (ascending) array
  @returns {array} quartiles as a 2-element array