ABSTRACT
In the 1830s, the German physician and a founder of experimental psychology, Ernst Weber, studied how well people could discriminate differences in weight. Single-subject ABAB-type experiments are used in the areas of psychology that little depend on a person's history such as sensation and perception: how well people can judge weights or the brightness of a light, or how they respond to visual displays, for example. The method in learning studies at the time was to compare groups of animals, to give one group a 'standard' treatment; and apply the treatment to be assessed to the other, experimental group. Numerous transfer experiments show that every learning experience has some lasting effect. The certainty and precision that can be achieved in R. A. Fisher's tea-lady experiment is almost never found in the statistical procedures that have become standard in much of social, medical, and environmental science.
