For instance, a simple sentence like "Show me the meal" has the gold standard parse: (S (VP (VB Show) (NP (PRP me)) (NP (DT the) (NN meal)))) and is parsed by this algorithm as (ROOT (VVB Show) (PNP me) (NP (AT0 the) (NN1 meal))) According to this evaluation scheme its recall is only 33%, because of the presence of the nonbranching rules, though intuitively it has correctly identified the bracketing.
the crossing brackets measures overvalues these algorithms, since they produces only partial parses -for some sentences my algorithm produces a completely flat parse tree which of course has no crossing brackets.