assertThrows(IllegalStateException.class, () -> EMPTY_STATS_VARARGS.populationVariance());
    assertThrows(IllegalStateException.class, () -> EMPTY_STATS_ITERABLE.populationVariance());
    assertThat(ONE_VALUE_STATS.populationVariance()).isEqualTo(0.0);
    assertThat(Stats.of(POSITIVE_INFINITY).populationVariance()).isNaN();
    assertThat(Stats.of(NEGATIVE_INFINITY).populationVariance()).isNaN();
    assertThat(Stats.of(NaN).populationVariance()).isNaN();

    assertThrows(IllegalStateException.class, () -> emptyAccumulator.populationVariance());
    assertThrows(
        IllegalStateException.class,
        () -> emptyAccumulatorByAddAllEmptyIterable.populationVariance());
    assertThrows(
        IllegalStateException.class, () -> emptyAccumulatorByAddAllEmptyStats.populationVariance());
    assertThat(oneValueAccumulator.populationVariance()).isEqualTo(0.0);

    assertThrows(IllegalStateException.class, () -> emptyAccumulator.populationVariance());
    assertThrows(
        IllegalStateException.class,
        () -> emptyAccumulatorByAddAllEmptyIterable.populationVariance());
    assertThrows(
        IllegalStateException.class, () -> emptyAccumulatorByAddAllEmptyStats.populationVariance());
    assertThat(oneValueAccumulator.populationVariance()).isEqualTo(0.0);

   */
  public final double sum() {
    return mean * count;
  }

  /**
   * Returns the <a href="http://en.wikipedia.org/wiki/Variance#Population_variance">population
   * variance</a> of the values. The count must be non-zero.
   *
   * <p>This is guaranteed to return zero if the dataset contains only exactly one finite value. It

   */
  public double sum() {
    return mean * count;
  }

  /**
   * Returns the <a href="http://en.wikipedia.org/wiki/Variance#Population_variance">population
   * variance</a> of the values. The count must be non-zero.
   *
   * <p>This is guaranteed to return zero if the dataset contains only exactly one finite value. It