This is because senior management is responsible for defining and communicating the IT strategy, objectives, and performance expectations for the organization. Senior management is also responsible for establishing and overseeing the IT governance framework, which includes the performance measurement metrics, processes, and tools. Senior management should ensure that the performance measurement metrics are aligned with the business goals and value creation, as well as the IT governance principles and policies. Senior management should also monitor and evaluate the IT performance results and take corrective actions if needed.

Some of the sources that support this answer are:

1: This source explains the roles and responsibilities of senior management in IT governance, and how they can use COBIT 5 to implement effective IT governance practices. It states that senior management should define the IT-related goals and objectives, establish the ITgovernance structure and processes, assign roles and responsibilities, and ensure adequate resources and capabilities for IT governance.

2: This source discusses the importance and benefits of IT performance measurement for IT governance, and provides some tips and tools for conducting it. It suggests that senior management should be involved in setting the IT performance measurement criteria, selecting the key performance indicators (KPIs), defining the targets and thresholds, and reviewing and reporting the IT performance outcomes.

3: This source provides a comprehensive guide on how to optimize IT project intake, approval, and prioritization. It mentions that senior management should be responsible for defining the strategic alignment, value delivery, risk optimization, and resource optimization criteria for IT projects, as well as for monitoring and evaluating the IT project portfolio performance.