The predicted LC50 values using our optimized QSAR regression model followed by the k-means clustering categorization resulted in 81% consistent classification between the acute fish toxicity categories generated by the direct classification method (Figure ). On the other hand, the predicted LC50 values using the model developed by Aalizadeh et al 34 resulted in only 37% consistent toxicity categories. This may be due to the fact that our QSAR regression and direct classification models both had the same training set as well as the fact that our QSAR regression model uses 8 descriptors while the model by Aalizadeh et al uses only 6 from which three are logP values.