function incrme() {
	var mean = incrmean();
	return accumulator;

	/**
	* If provided input values, the accumulator function returns an updated mean error. If not provided input values, the accumulator function returns the current mean error.
	*
	* @private
	* @param {number} [x] - input value
	* @param {number} [y] - input value
	* @returns {(number|null)} mean error or null
	*/
	function accumulator( x, y ) {
		if ( arguments.length === 0 ) {
			return mean();
		}
		return mean( y-x );
	}
}
Returns an accumulator function which incrementally computes the mean error.

@returns {Function} accumulator function

@example
var accumulator = incrme();

var m = accumulator();
// returns null

m = accumulator( 2.0, 3.0 );
// returns 1.0

m = accumulator( -5.0, 2.0 );
// returns 4.0

m = accumulator();
// returns 4.0