Figure 2 Power of likelihood ratio, log-rank, and Fisher’s exact tests as a function of the relative risk (RR) for different proportions of susceptible animals. Solid lines denote the likelihood ratio test; long dashes, the log-rank test; and short dashes, Fisher’s exact test. Simulations assume equal allocation to the vaccine and control arms of the study, a total sample size of N=50, a c<sub>max</sub> (maximum no. of challenges per animal) of 10, and p<sub>0</sub>=0.5 as the per-challenge probability of infection for control animals. The horizontal gray line denotes the significance level α=0.05 From: Power to Detect the Effects of HIV Vaccination in Repeated Low-Dose Challenge Experiments J Infect Dis. 2009;200(4):609-613. doi:10.1086/600891 J Infect Dis | © 2009 by the Infectious Diseases Society of America 1