Accordingly, the parameter k in Eq. 9 was set to (1.15+1) = 2; i.e., we may select the results of the first two orders of the predicted metabolic pathway classes for the query compounds. As we can see from Figure 1 , the accuracies of both the 1 st and 2 nd order predictions are higher than that of the random guess. According to Eq. 9 the metabolic pathway classes predicted by the 1 st and 2 nd orders have actually covered more than 80% of all the true metabolic pathway classes, suggesting that, of the results predicted by the 11 orders, more attention should be paid to those by the first two orders.