Subject: QSAR and scrambling

From: "O.Nicolotti" <[email-masked]>
Date: Sat, 13 Oct 2001 15:08:46 +0100

Hy everybody,
I would like to know your opinion about scrambling the activities 
data for validating QSAR models.
 
Usually, after scrambling affinity data, the classical statistics 
parameters (r2 and q2) are supposed to go dramatically down if the 
original QSAR models was a reliable model.

Anyway, if you are dealing with CoMFA, I would expect bad q2 
after scrambling but the r2 could also be still quite high since r2 
tend to be high when the number of descriptors is very large as it is 
in the CoMFA grid.
In other word while q2 must to go down, r2 values should not mean 
anything of relevant for validating the QSAR models. 

Any comment is very welcome.

Orazio