code: public double getStandardDeviationA() {
  		if(standardDeviationA == null) {
  			standardDeviationA = Math.sqrt(observationA.getMoments().get(2));
  		}
  		return standardDeviationA;
  	}
docs: Returns the standard deviation of the first value distribution.<br>
  The standard deviation shows the variation/dispersion from the average.<br>
  A low standard deviation indicates that the data points tend to be very close to the mean,<br>
  whereas high standard deviation indicates that the data are spread out over a large range of values.<br>
  @return The standard deviation of the first value distribution