/**
  * Get the Variance of all the stats that are watched, for all the stats added with add() since
  * the last call to clear() (in JSON).
  *
  * @return The Variance of all the stats since last clear() in JSON.
  */
 public String getVarianceJSON() {
   String str =
       String.format(
           FakeUserStats.jsonMediaStreamStatsTemplate,
           -1, // ssrc not needed here
           downloadJitterMs.getVariance(),
           downloadPercentLoss.getVariance(),
           downloadRateKiloBitPerSec.getVariance(),
           jitterBufferDelayMs.getVariance(),
           jitterBufferDelayPackets.getVariance(),
           nbDiscarded.getVariance(),
           nbDiscardedFull.getVariance(),
           nbDiscardedLate.getVariance(),
           nbDiscardedReset.getVariance(),
           nbDiscardedShrink.getVariance(),
           nbFec.getVariance(),
           nbPackets.getVariance(),
           nbPacketsLost.getVariance(),
           nbReceivedBytes.getVariance(),
           nbSentBytes.getVariance(),
           packetQueueCountPackets.getVariance(),
           packetQueueSize.getVariance(),
           percentDiscarded.getVariance(),
           rttMs.getVariance(),
           uploadJitterMs.getVariance(),
           uploadPercentLoss.getVariance(),
           uploadRateKiloBitPerSec.getVariance());
   return str;
 }