Which of the following roles helps to evaluate the effectiveness of group discussions?

The role of the evaluator-critic in group discussions is pivotal as it involves assessing the group's communication and decision-making processes. This role is primarily concerned with analyzing the contributions of the group members, providing feedback on the effectiveness of the discussion, and identifying areas for improvement. The evaluator-critic helps ensure that the dialogue remains constructive and on track, fostering a more productive environment.

By evaluating the group's progress and the quality of ideas presented, the evaluator-critic encourages reflection among group members about their interaction patterns and the outcomes of their discussions. This reflective practice can enhance the overall efficiency of the group's work and help members develop better communication strategies in future discussions.

The other roles, while important, focus more on initiating conversation, organizing contributions, or expanding upon ideas, rather than critically assessing the discussion itself. Thus, the evaluator-critic distinctly fulfills the need for a role dedicated to the analysis and improvement of the group's communicative effectiveness.