Alternative Definitions of Sensitivity

The term sensitivity can unfortunately create some confusion, since it is sometimes defined as the ratio of absolute changes, i.e., AY/AX. In the limit, this becomes dY/dX, so that this particular sensitivity is the slope of a graph of response vs stimulus. An example of this definition is the sensitivity of tissues to hormones, e.g., the sensitivity of adipose tissue to insulin. In contrast, the sensitivity used throughout this article is the slope of a graph of log Y vs log X [Eq. (3), Section III, A]. A problem is that the two definitions give different results when sensitivities are compared so that an opportunity for confusion, due solely to semantics, may develop. For example, the responses of two enzymes, Ej and E2, to a substrate, S [for simplicity, Michaelis-Menten responses are assumed 

It might be beneficial to restrict sensitivity to the definition based on relative changes, as in this article. The alternative function could be expressed in some other way for example as potency. Thus referring to Fig. 6, the potency of activation by the concentration of S is greater for Ej (or, S is a more potent activator of Ex), whereas the sensitivity of the response to the concentration of S is the same for both enzymes. 

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The method of defining RSFs described is traditional in analytical chemistry, generates RSFs without units, results in larger numbers for elements for which the SIMS instrument is more sensitive, and is essentially the same as Wittmaack s proposed use of scaled sensitivity ratios [100]. However, an alternative definition of sensitivity factors that has gained much popularity with semiconductor specialists is that of Wilson [69,101] ... 

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