F-Test
	q F-distribution is non-symmetric. q There are two critical F values of unequal magnitude. q Whether to use the upper or the lower critical value depends on the relative magnitudes of S1 and S2:      If S1 > S2, then use the upper limit FU to reject the null hypothesis      If S1 < S2, then use the lower limit FL to reject the null hypothesis q Or you can always make S1 > S2 when F is defined. In this case, you can always use the upper limit to examine the hypothesis.