compensation effect

In a considerable number of cases plots of $Math - ei$ vs. $Math - ei$ , for a series of reactions, e.g. for a reaction in a range of different solvents, are straight lines of approximately unit slope. Therefore, the terms $Math - ei$ and $Math - ei$ in the expression partially compensate, and

$Math - e$

often is a much simpler function of solvent (or other) variation than $Math - ei$ or $Math - ei$ separately.