Improved confidence limits for low-dose carcinogenic risk assessment from animal data

An improved procedure is presented for estimating low-dose risks from dichotomous animal data. Based on the multistage model of cancer, the procedure gives a maximum likelihood fit to the experimental data. Because the model is approximately linear in the low-dose range, the procedure may be considered to be a generalized method for linear extrapolation which uses all of the data. The extrapolation procedure is different from an earlier procedure based upon the multistage model in that two improved methods are put forward for calculating statistical confidence limits. (One is a linearized approximation of the other.) A further innovation is a recommendation for the integration of several data sets in the calculation of risk levels.