CoMFA series design

Most QSAR and 3D QSAR studies are retrospective analyses without an appropriate series design. The consequences are either a poor fit of the training set data or a lack of predic-tivity for the test set compounds. The poor predictivity of the CBG CoMFA models (compounds 1 and 2 Section 2.3) is not surprising if one considers that compound 23 is the only one in the whole data set which bears a 21-acetoxy group and that also compound 31, a 9-fluoro-substituted steroid, is outside the structural space of the training set. 

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