public function getVariance() {
		if ( $this->n === 0 ) {
			// The variance of the empty set is undefined.
			return NAN;
		} elseif ( $this->n === 1 ) {
			return 0.0;
		} else {
			return $this->m2 / ( $this->n - 1.0 );
		}
	}
public function getVariance() {
		if ( $this->n === 0 ) {
			// The variance of the empty set is undefined.
			return NAN;
		} elseif ( $this->n === 1 ) {
			return 0.0;
		} else {
			return $this->m2 / ( $this->n - 1.0 );
		}
	}
public function getVariance ( ) { if ( $ this -> n === 0 ) { // The variance of the empty set is undefined. return NAN ; } elseif ( $ this -> n === 1 ) { return 0.0 ; } else { return $ this -> m2 / ( $ this -> n - 1.0 ) ; } }
Get the estimated variance.

Variance measures how far a set of numbers is spread out. A small
variance indicates that the data points tend to be very close to the
mean (and hence to each other), while a high variance indicates that the
data points are very spread out from the mean and from each other.

@return float Estimated variance
Get the estimated variance .