code: public final double getMeanDeviation()
      {
          double mean = getArithmeticMean();
          double diffs = 0;
          for (int i = 0; i < dataSetSize; i++)
          {
              diffs += Math.abs(mean - dataSet[i]);
          }
          return diffs / dataSetSize;
      }
docs: Calculates the mean absolute deviation of the data set.  This
  is the average (absolute) amount that a single value deviates from
  the arithmetic mean.
  @see #getArithmeticMean()
  @see #getVariance()
  @see #getStandardDeviation()
  @return The mean absolute deviation of the data set.
  @throws EmptyDataSetException If the data set is empty.