THE LOG TRANSFORMATION IS SPECIAL

The logarithmic (log) transformation is a simple yet controversial ste p in the analysis of positive continuous data measured on an interval scale. Situations where a log transformation is indicated will be revi ewed. This paper contends that the log transformation should not be cl assed with other transformations as it has particular advantages. Prob lems with using the data themselves to decide whether or not to transf orm will be discussed. It is recommended that log transformed analyses should frequently be preferred to untransformed analyses and that car eful consideration should be given to use of a log transformation at t he protocol design stage.