The Additivity Model Free Wilson Analysis

The Free Wilson model was in its original formulation [16] not as simple. No reference compound was selected and so-called symmetry equations were generated to avoid the problem of linear dependences between the variables. 

The version described by Fujita and Ban (eq. 8, chapter 1.1) [20, 390, 391] is a straightforward application of the additivity concept of group contributions to biological activity values. As nowadays only this modification is used, no details of the original formulation of the Free Wilson model and its complicated symmetry equations are discussed here. 

In comparison with the classical version of the Free Wilson analysis, the Fujita Ban variant offers a number of important advantages  

The addition and elimination of compounds is simple and does not change the values of the other regression coefficients significantly. 

Substituents which always occur together in two different positions of the molecule can be combined to a pseudosubstituent. 

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