Biological variability allowable

Attention should be paid to the sufficiency of the study with respect to determining significance and assessing hazard, eg, whether the number of control and test animals is sufficient to allow detection of biological variability in response and for comparative statistical procedures. 

All data obtained by these novel techniques require a very deep and multifaceted analysis, in order to check the principal and fundamentals variables and to reject the others. In this scenario, chemometrics provide scientists with useful tools to interpret the large amounts of data generated by these complex analytical assays and allows for quality control, classification procedures, modelling studies. Discrimination between different molecules available as novel drugs and molecules having no interesting biological activities is easy by means of multivariate analysis. 

Other problems with the Hansch method are that biological systems are often too crude as models for its application, or the electronic effects operative in a drug molecule are not sufficiently understood or precise. Finally, the method requires considerable time and expense, even in the hands of an expert. Difficulties notwithstanding, the Hansch approach took both chemists and pharmacologists out of the dark age of pure empiricism and allowed them to consider simultaneously the effects of a large number of variables of drug activity—a feat unattainable with classical methods. 

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