+ (values.xStats().mean() - xStats.mean())
                  * (values.yStats().mean() - yStats.mean())
                  * values.count();
    }
    yStats.addAll(values.yStats());
  }

  /** Returns an immutable snapshot of the current statistics. */
  public PairedStats snapshot() {
    return new PairedStats(xStats.snapshot(), yStats.snapshot(), sumOfProductsOfDeltas);
  }

    assertStatsApproxEqual(TWO_VALUES_STATS, TWO_VALUES_PAIRED_STATS.xStats());
    assertStatsApproxEqual(MANY_VALUES_STATS_ITERABLE, MANY_VALUES_PAIRED_STATS.xStats());
  }

  public void testYStats() {
    assertStatsApproxEqual(EMPTY_STATS_ITERABLE, EMPTY_PAIRED_STATS.yStats());
    assertStatsApproxEqual(OTHER_ONE_VALUE_STATS, ONE_VALUE_PAIRED_STATS.yStats());

    assertStatsApproxEqual(TWO_VALUES_STATS, TWO_VALUES_PAIRED_STATS.xStats());
    assertStatsApproxEqual(MANY_VALUES_STATS_ITERABLE, MANY_VALUES_PAIRED_STATS.xStats());
  }

  public void testYStats() {
    assertStatsApproxEqual(EMPTY_STATS_ITERABLE, EMPTY_PAIRED_STATS.yStats());
    assertStatsApproxEqual(OTHER_ONE_VALUE_STATS, ONE_VALUE_PAIRED_STATS.yStats());

    assertStatsApproxEqual(EMPTY_STATS_ITERABLE, emptyAccumulator.xStats());
    assertStatsApproxEqual(EMPTY_STATS_ITERABLE, emptyAccumulatorByAddAllEmptyPairedStats.xStats());
    assertStatsApproxEqual(ONE_VALUE_STATS, oneValueAccumulator.xStats());
    assertStatsApproxEqual(ONE_VALUE_STATS, oneValueAccumulatorByAddAllEmptyPairedStats.xStats());
    assertStatsApproxEqual(TWO_VALUES_STATS, twoValuesAccumulator.xStats());

    assertStatsApproxEqual(EMPTY_STATS_ITERABLE, emptyAccumulator.xStats());
    assertStatsApproxEqual(EMPTY_STATS_ITERABLE, emptyAccumulatorByAddAllEmptyPairedStats.xStats());
    assertStatsApproxEqual(ONE_VALUE_STATS, oneValueAccumulator.xStats());
    assertStatsApproxEqual(ONE_VALUE_STATS, oneValueAccumulatorByAddAllEmptyPairedStats.xStats());
    assertStatsApproxEqual(TWO_VALUES_STATS, twoValuesAccumulator.xStats());

   *
   * <ul>
   *   <li>Both {@code xStats} and {@code yStats} must have the same {@code count}.
   *   <li>If that {@code count} is 1, {@code sumOfProductsOfDeltas} must be exactly 0.0.
   *   <li>If that {@code count} is more than 1, {@code sumOfProductsOfDeltas} must be finite.
   * </ul>
   */
  PairedStats(Stats xStats, Stats yStats, double sumOfProductsOfDeltas) {
    this.xStats = xStats;
    this.yStats = yStats;

		return 0
	}

	stats.RLock()
	defer stats.RUnlock()

	val, ok := stats.apiStats[api]
	if ok {
		return val
	}

	return 0
}

// Load returns the recorded stats.
func (stats *HTTPAPIStats) Load(toLower bool) map[string]int {
	if stats == nil {
		return map[string]int{}
	}

	stats.RLock()
	defer stats.RUnlock()

	if len(r.mostRecentStats.Stats) == 0 {
		r.mostRecentStats = BucketStatsMap{Stats: make(map[string]BucketStats, 1), Timestamp: UTCNow()}
	}
	if len(bs.ReplicationStats.Stats) > 0 {
		r.mostRecentStats.Stats[bucket] = bs
	}
	r.mostRecentStats.Timestamp = UTCNow()
	r.mostRecentStatsMu.Unlock()
	return bs
}

// get the most current of in-memory replication stats  and data usage info from crawler.

	qs.QStats = r.qCache.getSiteStats()

	r.RLock()
	defer r.RUnlock()
	tx := newXferStats()
	for _, brs := range r.Cache {
		for _, v := range brs.Stats {
			tx := tx.merge(*v.XferRateLrg)
			tx = tx.merge(*v.XferRateSml)
		}
	}
	qs.XferStats[Total] = *tx
	return qs
}

// ReplicationQueueStats holds overall queue stats for replication

		}
		switch msgp.UnsafeString(field) {
		case "Stats":
			var zb0002 uint32
			zb0002, err = dc.ReadMapHeader()
			if err != nil {
				err = msgp.WrapError(err, "Stats")
				return
			}
			if z.Stats == nil {
				z.Stats = make(map[string]*BucketReplicationStat, zb0002)
			} else if len(z.Stats) > 0 {
				for key := range z.Stats {
					delete(z.Stats, key)
				}
			}
			for zb0002 > 0 {