A project manager is tracking project performance, but a key stakeholder refuses to accept the project's KPI results. Which tool or technique should the project manager use?

Expert judgment is the best tool or technique here because it involves consulting individuals or groups with specialized knowledge or training in a specific area. In this scenario, an expert can help analyze the KPI results, explain their validity, or identify any discrepancies or misunderstandings the stakeholder might have. This approach facilitates understanding and can build consensus. Change control tools are used for managing changes to the project baselines, not for resolving stakeholder disagreements over performance data. Autocratic decision-making would likely worsen the stakeholder relationship and not address the underlying issue of their refusal to accept the results. A context diagram is a visual representation of a system and its external interfaces, which is irrelevant to resolving a dispute over KPI results.