Using the reranker features distributed with the Brown reranker (Charniak and Johnson, 2005), which we call the "standard" set below, we obtained no overall improvement in f-score when either reranking the Berkeley parser n-best lists alone, or when the Berkeley parses were combined with the Brown parses.
it is possible that these results reflect the fact that the features used by the reranker were chosen because they improve the Brown parser, i.e., they are the result of feature selection based on reranking the Brown parser's n-best lists.