text: Animal models are used to learn more about a disease, its diagnosis and its treatment, with animal models predicting human toxicity in up to 71% of cases. The human equivalent dose (HED) or human equivalent concentration (HEC) is the quantity of a chemical that, when administered to humans, produces an effect equal to that produced in test animals by a smaller dose. Calculating the HED is a step in carrying out a clinical trial of a pharmaceutical drug.