The changing of a variable or expression to a mathematical form of another type - e.g. the variable x can be transformed to ...x3, x2, x0.5, log10x, lnx, etc. 1) biological processes like growth are multiplicative, and thus do not proceed in a linear way 2) statistical power can increase in transformed data because transformations can lead to normality and then we can then use parametric tests. [Log transformations are used if: greater means are accompanied by greater variances; the data are skewed to the right; effects are multiplicative.]