private double variance() {
		double ave = average();
		double var = 0, sum = 0, number = 0;
		for (Patient p : this.allPatients) {
			if (!p.isHospitalized()) {
				sum += Math.pow(ave - p.getTotalTime(), 2.0);
				number++;
			}
		}

		var = sum / number;
		return var;
	}