_incrementSampled() {
    if (++this._sampled >= this._samplingTarget) {
      // For the first sample window we take the first 10 transactions and only
      // the first 10.
      let adjustedTarget = 0
      if (this._resetCount > 0) {
        const target = this._samplingTarget
        const ratio = target / this._sampled
        const max = target / this._maxSamples
        adjustedTarget = Math.pow(target, ratio) - Math.pow(target, max)
      }
      this._adjustStats(adjustedTarget)
    }
  }
Increments the sampled counter and adjusted the sampling threshold to maintain
a steady sample rate.