Cumulative Record. Chapter 35: Two Types of Conditioned Reflex and a Pseudo-type. Quote 3

… the magnitude of the response in an operant is not a measure of its strength. Some other measure must be devised, and from the definition of an operant it is easy to arrive at the rate of occurrence of the response. This measure has been shown to be significant in a large number of characteristic changes in strength. (p. 539)