Illustrating the context of dose-finding designs such as up-and-down. Observations are dichotomized to positive/negative, and the probability of positive response increases with increasing dose. Estimating the entire dose–response curve F(x) requires numerous observations throughout the dose range, including doses that might be too low or too high for patient needs. Dose-finding designs concentrate most observations in a region of interest; illustrated are two often-targeted regions: the ED50 or minimum alveolar concentration (MAC) and the ED90.