The most common errors are predicting B for chunks labeled O and confusing tags B and C. Manually inspecting the pictures in our training set shows that annotators often omitted the verb (such as "is" or "has") and left the B position empty, since it could be inferred by the presence of the arrow and the images in A and C. Also, annotators tended to disagree on the location of adverbial expressions, dividing them between positions B and C. Finally, only 3.3% of chunks were incorrectly omitted from the pictures.
we conclude that our CRF models are capable of predicting the ABC layouts.