Use of the logistic function for the calculation of dose-ratios and potency ratios

1 Dose-ratios and potency ratios, obtained with the guinea-pig isolated ileum by calculating matching concentrations from a least-squares fit using a logistic relationship between response and dose, differ from those obtained with the more usual assumption that response is a linear function of log dose over a limited range. 2 The differences are not due to the mathematical treatment of the results but arise from changes in sensitivity associated with the production of very high or very low responses. 3 With this preparation there is no advantage in avoiding the linear transformation and fitting the results to the complete dose-response curve though this might not apply to results obtained from other tissues with less variable sensitivity.