Unsupervised Grammar Induction with Depth-bounded PCFG
Table 5: PARSEVAL scores for all competing systems on WSJ10 and WSJ20 test sets. These are unlabeled precision, recall and F1 scores on constituent trees without punctuation (**: p <0.0001, permutation test).
['System', 'WSJ10test Precision', 'WSJ10test Recall', 'WSJ10test F1', 'WSJ20test Precision', 'WSJ20test Recall', 'WSJ20test F1']
The right-branching baseline is relatively weak on these two datasets, mainly because formal writing is more complex and uses more non-right-branching structures (e.g., subjects with modifiers or parentheticals) than child-directed speech. For WSJ10test, both the DB-PCFG system and CCL are able to outperform the right branching baseline. The F1 difference between the best-performing previous-work system, CCL, and DB-PCFG is highly significant. For WSJ20test, again both CCL and DB-PCFG are above the right-branching baseline. The difference between the F scores of CCL and DB-PCFG is very small compared to WSJ10, however it is also significant.