We can see from both Tables 3 and 4 that when the number of words in a sequence is small, the result has no effect with the number of positive training data, since the range of F-score in Table 3 is 0.415 ∼ 0.478, and that in Table 4  is 0.453 ∼ 0.516.
as we can see from Table 2, when the number of title words is large, the smaller the number of positive training data is, the worse the result is.