docs: @Override
      public double getStandardDeviation() {
          double stdDev = Double.NaN;
          if (getN() > 0) {
              if (getN() > 1) {
                  stdDev = FastMath.sqrt(getVariance());
              } else {
                  stdDev = 0.0;
              }
          }
          return stdDev;
      }