When is Self Training Effective for Parsing?
Self training has been shown capable of improving on state of the art parser performance (McClosky et al. 2006) despite the conventional wisdom on the matter and several studies to the contrary (Charniak, 1997; Steedman et al. 2003) However, it has remained unclear when and why self training is helpful. In this paper, we test four hypotheses (namely, presence of a phase transition, impact of search errors, value of non generative reranker features, and effects of unknown words) From these experiments, we gain a better understanding of why self training works for parsing. Since improvements from self training are correlated with unknown bigrams and biheads but not unknown words, the benefit of self training appears most influenced by seeing known words in new combinations.
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