One difficulty concerns multi-word expressions that the campaign managers finally chose to annotate both as multi-word expressions and as distinct elements to avoid "linguistic debates".
the first method consists in measuring the residual ambiguity degree by observing the traces left by the annotator during the annotation: the annotation protocol may allow the annotator to annotate with several labels in case of ambiguity, to use an under-determined label, or even to add an uncertainty feature to the chosen label.