code: public double getVariance() {
          if (!DATA_LIST.isEmpty()) {
              double sum = 0;
              double sumOfSquares = 0;
              double average = 0;
              for (DataPoint dataPoint : DATA_LIST) {
                  sumOfSquares += (dataPoint.getValue() * dataPoint.getValue());
                  sum += dataPoint.getValue();
              }
              average = sum / DATA_LIST.size();
              return (sumOfSquares / DATA_LIST.size()) - average * average;
          }
          return 0;
      }
docs: Returns the calculated varianz of the current data
  @return the calculated varianz of the current data