In the example in Figure 2, the vandalism diff text will probably score low, because although it shares an overlap bigram "and roll" with the phrase "rock and roll" in training text, once we apply the shallow syntactic n-gram modeling method, the POS tag bigram "and/CC roll/VB" in diff text will be distinguished from the "and/CC roll/NN" or "and/CC roll/NNP" in the training data.
their average recall is not very high and they can be easily fooled by unseen vandalism patterns.