However, since the boundaries of the spans annotated in the MPQA corpus are not strictly defined in the annotation guidelines (Wiebe et al., 2005), measuring precision and recall using exact boundary scoring will result in figures that are too low to be indicative of the usefulness of the system.
most work using this corpus instead use overlap-based precision and recall measures, where a span is counted as correctly detected if it overlaps with a span in the gold standard (Choi et al., 2006;Breck et al., 2007).