Fig. 1.
Types of concentration (or dose)–response curves. (Left) Graded curve, showing percentage of maximum response (efficacy) in a single unit (e.g., cell, organ, animal, or human). The dose (or concentration) of drug producing a half-maximum effect is the ED50 or EC50. (Right) Quantal curve, showing the percentage of a study population showing a response to an all-or-nothing outcome. The dose (or concentration) of drug needed to produce a quantal response in 50% of the population is the ED50 or EC50 (also known as the median dose or concentration).