The poor statistical properties of the Fe-plot.

The poor statistical properties of the Fe-plot as a method of estimating the alpha/beta ratio in the linear quadratic model for multifraction data are summarized. A Monte Carlo simulation of quantal response data shows that the Fe-plot method of analysis is about half as efficient as logistic regression, indicating that twice the amount of data would be needed to obtain the same accuracy in the estimate of alpha/beta if the Fe-plot was used rather than logistic regression. In addition, the confidence intervals from the Fe-plot are inappropriately too narrow and do not have the correct coverage rate. Model-based statistical methods which directly link the treatment variables, dose and number of fractions to the response are advocated.