for distribution of the solute between octan-1-ol and water. The most general way of applying 
in correlation analysis, QSAR, etc. is as log 
, but the behaviour of substituted benzene derivatives may be quantified by a substituent constant scale, 
, which is defined in a way analogous to the Hammett σ scale. There are various scales, depending on the substrate series used as reference. Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1119