The relationships between the linear free energy related Hansch model and the mathematical models of Free-Wilson and Bocek-Kopecký are reviewed and discuss. Some examples are given to illustrate the theoretically derived relationships and to demonstrate scope and limitations of each mathematical model. The modified Free-Wilson approach is shown to be completely equivalent to a nonparabolic Hansch approach; it can be used to study additivity or nonadditivity of group contributions and to control and improve the fitting of Hansch equations. The Bocek-Kopecký approach is related to the parabolic form of the Hansch approach; its practial use is limited by the great number of variables involved.