What measure has contributed to reducing the second increment slippage?

The choice that reflects a significant contribution to reducing second increment slippage is implementation of automated testing. Automated testing can greatly enhance the efficiency and effectiveness of the testing process. It allows for faster execution of tests, especially for repetitive tasks, and ensures consistent test execution.

By utilizing automated testing, the team can quickly identify issues and regressions, which helps in meeting tight timelines and reducing the likelihood of slippage in a project increment. This efficiency can shift focus towards more complex testing scenarios that may require human insight, ultimately helping the test team to stay on schedule.

In contrast, increased overtime, while it may provide a temporary solution, can lead to burnout and decreased productivity over time. Training of team members can improve long-term capabilities but may not have an immediate impact on slippage. Relaxing requirements could potentially lead to more significant issues down the line, as it may compromise quality and lead to even greater risks in future increments. Therefore, automation stands out as the most effective measure to reduce slippage in the context provided.