code: public Double getSurvivalTimePercentile(String group, double percentile) {
  
  		StrataInfo si = sfi.getStrataInfoHashMap().get(group);
  		ArrayList<Double> percentage = si.getSurv();
  		Integer percentileIndex = null;
  		for (int i = 0; i < percentage.size(); i++) {
  			if (percentage.get(i) == percentile) {
  				if (i + 1 < percentage.size()) {
  					percentileIndex = i + 1;
  				}
  				break;
  			} else if (percentage.get(i) < percentile) {
  				percentileIndex = i;
  				break;
  			}
  		}
  		if (percentileIndex != null) {
  			return si.getTime().get(percentileIndex);
  		} else {
  			return null;
  		}
  	}
docs: To get the median percentile for a particular group pass the value of
  .50.
  
  @param group
  @param percentile
  @return