It is generally not possible to directly compare quantitative results because of vast differences in methodology, tag set, type and amount of training data, and, principally, assumptions made about what information is available for "free" (e.g., hand-transcribed versus automatically recognized words, or segmented versus unsegmented utterances).
we will focus on the conceptual aspects of previous research efforts, and while we do offer a summary of previous quantitative results, these should be interpreted as informative datapoints only, and not as fair comparisons between algorithms.