public double sampleVariance(int nt) {
		if( (nt < 1) || (nt > n) ) return 0;

		double mean = mean(nt);
		double sum = 0;
		for( int ns = 0; ns < numberOfSamples; ns++ ) {
			double d = rankSum[ns][nt - 1] - mean;
			sum += d * d;
		}
		double var = sum / ((numberOfSamples - 1));

		return var;
	}