@Override
  protected DescriptiveStatistics statistics(
      Collection<? extends Person> persons, String purpose, String mode) {
    DescriptiveStatistics stats = super.statistics(persons, purpose, mode);

    if (threshold > 0) {
      DescriptiveStatistics newStats = new DescriptiveStatistics();
      for (int i = 0; i < stats.getN(); i++) {
        double val = stats.getElement(i);
        if (val >= threshold) {
          newStats.addValue(val);
        }
      }

      return newStats;
    } else {
      return stats;
    }
  }