Methods for evaluating dependency parsing using attachment scores are highly sensitive to representational variation between dependency treebanks, making cross-experimental evaluation opaque. This paper develops a robust procedure for cross-experimental evaluation, based on deterministic unification-based operations for harmonizing different representations and a refined notion of tree edit distance for evaluating parse hypotheses relative to multiple gold standards. We demonstrate that, for different conversions of the Penn Treebank into dependencies, performance trends that are observed for parsing results in isolation change or dissolve completely when parse hypotheses are normalized and brought into the same common ground.
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