In all the three figures, the same trend can be observed: Step by step, the median of F1-score distributions get worse as the percentage increases. Especially when more than half of the words were replaced or removed, the tendency for the classification results to become worse became particularly obvious. In addition, the variance of the F1-scores always becomes larger, if a certain percentage of words in texts are replaced or removed. According to the Welch’s t-test, in all cases, whether the words are replaced or removed does not affect the classification. This observation indicates that the POS-tags do not contribute to the distinction of authorships.