protected double computeConfidence() {
   return 1 - Math.pow(.9, elts);
 }
  protected double computeConfidence() {

    return 1 - Math.pow(.5, ppt.num_samples());
  }
 public int derivedDepth() {
   return 1 + Math.max(base1.derivedDepth(), Math.max(base2.derivedDepth(), base3.derivedDepth()));
 }