Figure 11.9: Figure 11.6 Sampling Distribution of F for Effect of Surgery and Physical Therapy on Back Pain Fcv of 6.013 is the boundary between the common zone and the rare zone for this sampling distribution of F with 2 and 18 degrees of freedom and α = .01. The null hypothesis is not rejected if the results fall in the common zone; it is rejected if results fall on the line or in the rare zone.