Which aspect of verification measures the effect before and after system upgrades?

Baseline performance assessment is the correct choice because it specifically focuses on measuring and documenting the performance of a system before and after any upgrades or changes. This process establishes a standard or "baseline" of how the system operates under normal conditions, allowing for a clear comparison after modifications.

When system upgrades are implemented, the baseline performance assessment helps to evaluate the impact of those upgrades by providing measurable data that can confirm whether the performance has improved, declined, or remained stable. This comparative analysis is crucial for understanding the effectiveness of the upgrades and making informed decisions about future modifications.

Operational testing is focused on the ongoing functionality of systems under real-world conditions, while post-installation reviews generally look at the overall installation process rather than specific performance metrics. Environmental impact assessments analyze the effects of a system on its surrounding environment, which is not about performance changes before and after upgrades.