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.
See also: isokinetic relationship
PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1098