We are surrounded by synthetic and natural substances that have positive or negative effect upon humans and animals. It is difficult to estimate the effects of a substance without testing it on living organisms. Chemical and physical properties tell us about the molecules themselves, but living organisms may react in unpredictable ways. That is why we use biological assay in short bioassay to estimate effects.

A bioassay involves measurement of the effect of a putative toxic substance on organisms or parts thereof.

“As a branch of applied statistics, biological assay appears to have a somewhat specialized
appeal. Although a few statisticians have worked in it intensively, to the majority it appears
as a topic that can be neglected, either because of its difficulties or because it is trivial. … . Despite this, I am convinced that many features of bioassay are outstandingly
good for concentrating the mind on important parts of biometric practice and
statistical inference.”
D. J. Finney Source: International Statistical Review / Revue Internationale de Statistique,Vol. 47, No. 1 (Apr., 1976), pp. 1-12

The Book: Dose-Response Analysis Using R