As to the following formulas which give the life span distribution of forest stands,
Case I F_k(t) = (M<(Mt)>^^^<k-1>)/((k-1)!) exp[-Mt]
Case II F_k(t) = (N(1-e^<ct>)^^^<k-1>)/((k-1)!) exp[-N(1-e^<-ct>)]Nce^<-ct>
Case III F_k(t) = (N!k)/((k-1)!(k-1)!) <(e^<-ct>)>^^^<N-k+1><(1-e^<-ct>)>^^^<k-1>
the auther showed the way to determine the "Gentan probability" q(j) and the parameters. That is, some trasformations lead the q(j) in Case I and II to the chi distribution with the degree of freedom 2k. In Case III q(j) is led to the F-distribution with the degree of freedom 2k and 2(N-k+1). And it was showed that the parameters can be calculated by the records of cutting and the data on the diameter growth of forest stands.