It is interesting to note that RSTbased discourse features generally have higher correlations with the holistic speaking proficiency scores than with the more specific discourse coherence scores.
human annotators were trained in a two-step process: 1) after a comprehensive study of the annotation guidelines described in Section 3.1, the two annotators were initially trained with 16 TPO responses (8 responses from an Independent question and 8 responses from an Integrated question) by first performing independent annotation and then resolving all disagreements through a discussion of the guidelines; 2) another round of training was conducted on an additional set of 32 TPO responses (8 responses from an Independent question and 24 responses from an Integrated question).