A simplified method of evaluating dose-effect experiments.

1. A rapid graphic method for approximating the Median Effective Dose and the Slope of dose-per cent effect curves is presented. Confidence limits of both of these parameters for 19/20 probability are given by the method. In addition, confidence limits for any other probability or for a dose other than the Median Effective Dose are readily estimated. 2. The data are used throughout the method in their original form without transformation to logarithms and probits. 3. An effective means for plotting and using 0 and 100 per cent effects is provided. 4. The calculations have been simplified by means of nomographs to the extent that a slide rule is a convenience but not a necessity. 5. A simple means is provided for detecting a poorly fitted line or significantly heterogeneous data, In the former case, the line may be refitted; in the latter, the confidence limits are corrected for the degree of heterogeneity. 6. The method provides means for the rapid test of parallelism of two curves and easy computation of relative potency with its confidence limits. 7. Although the method is rapid (10-15 minutes), its accuracy is commensurate with the nature of dose-per cent effect data.