Which of the following is NOT a performance metric?

Data encryption methods are not considered a performance metric because they pertain to security rather than performance measurement. Performance metrics are typically quantitative measures used to evaluate the efficiency and speed of a system's operation, and they focus on how quickly and effectively the system performs tasks.

In contrast, screen load time, response time to user actions, and concurrent user capacity all directly pertain to how well the application runs and how it interacts with users. Screen load time measures how quickly a screen appears to the user, response time tracks how quickly the system reacts to user input, and concurrent user capacity indicates how many users can efficiently use the application at the same time. Each of these reflects aspects of system performance, making them relevant to evaluating an application's operational effectiveness, while data encryption methods ensure the safety and confidentiality of the data, which does not relate to performance measurements.