Group contribution has been to the prediction of solubility and logP values with high accuracy , however the application to biodegradability has been less straightforward. One reason is that the biodegradability values obtained tend to be less on a continuous scale, with many compounds exhibiting near-zero or complete biodegradability on this scale . The selection of vague identifiers like quaternary carbons without distinguishing sub-groups may also result in inaccurate coefficients. On the other hand, substructs that are too specific can overfit the available data and must be treated with caution.