Hi, I want to calculate, for any likelihood function, the value(s) of the parameter of interest that makes the likelihood equal to 1/8-th of the value of the likelihood at the maximum. Say, with the following toy example with a binomial distribution and with interest in p: p<-seq(0.01,0.99,by=0.001) n=113 y=28 llbin<-y*log(p)+(n-y)*log(1-p) #log-likelihood lbin<-exp(llbin) #likelihood rlbin<-mat.or.vec(length(p),nc=1) #relative-likelihood for (i in 1:length(p)) { rlbin[i]<-lbin[i]/max(lbin) } How do I obtain the value of p such that rlbin=0.125? It doesn't seem to me that I can do this using solve. I can do this rlbinp<-cbind(rlbin,p) rlbinp and actually look at the two values of p that make the rlbin go down to 0.125*max(rlbin), but there must be another way. The corresponding function in Octave (and Matlab) is fzero. Thanks in advance, Rub?n