where M j is the number of the compounds whose j-th order predicted metabolic pathway class is one of the true pathway classes that the compounds are involved with, and N is the total number of compounds in the dataset. Such 11-order accuracies were used to evaluate our prediction method. It is obvious according to the definition of Eq. 7 that, the higher the value of W j with a smaller value of j, or the lower the value of W j with a larger value of j, the better the prediction quality will be by our method.