Leonardo Journal of Sciences ISSN 1583-0233 Issue 9, July-December 2006 p. 179-200 179 http://ljs.academicdirect.org Pearson versus Spearman, Kendall's Tau Correlation Analysis on Structure-Activity Relationships of Biologic Active Compounds Sorana-Daniela BOLBOACĂ 1 , Lorentz J˜NTSCHI 2 1 Iuliu Haţieganu University of Medicine and Pharmacy, 13 Emil Isac, 400023 Cluj- Napoca, Romania; 2 Technical University of Cluj-Napoca, 15 Constantin Daicoviciu, 400020 Cluj-Napoca, Romania sbolboaca@umfcluj.ro , lori@academicdirect.org , Abstract A sample of sixty-seven pyrimidine derivatives with inhibitory activity on E. coli dihydrofolate reductase (DHFR) was studied by the use of molecular descriptors family on structure-activity relationships. Starting from the results obtained by applying of MDF-SAR methodology on pyrimidine derivatives and from the assumption that the measured activity (compounds inhibitory activity) of a biologically active compounds is a semi-quantitative outcome (can be related with the type of equipment used, the researchers, the chemical used, etc.), the abilities of Pearson, Spearman, Kendalls, and Gamma correlation coefficients in analysis of estimated toxicity were studied and are presented. Keywords Multiple linear regressions, Correlation coefficients, Molecular Descriptors Family on Structure-Activity Relationships (MDF-SAR) Introduction QSAR (Quantitative Structure-Activity Relationships) is an approach which is able to indicate for a given compound or a class of compounds which feature of structure characteristics is correlated with its activity [1]. In QSAR analysis were proposed several