A risk-based approach is being taken to test a new web-based retail application.

In a risk-based approach to testing, various roles and responsibilities are distributed among the team members. Here’s an analysis of the activities listed in the options:

A. Understanding the probability of each technical product risk: This is indeed within the scope of the Technical Test Analyst's responsibilities. They need to evaluate and understand the likelihood of technical risks to plan appropriate testing strategies.

B. Assessing the likelihood of identified security risks: This also falls under the Technical Test Analyst’s role, as they are expected to evaluate different types of risks, including security risks, and understand their likelihood.

C. Assessing the business impact of identified performance risks: This task is more aligned with the role of a Business Analyst or Product Owner. The business impact assessment usually requires a deep understanding of business operations, financial implications, and stakeholder priorities, which are typically beyond the technical focus of a Technical Test Analyst.

D. Designing tests to mitigate identified reliability risks: Designing tests to address reliability risks is a core activity for Technical Test Analysts. They are expected to create test cases and scenarios that target identified reliability issues to ensure the system’s stability and robustness.

Therefore, the activity that a Technical Test Analyst is NOT usually expected to perform is C. Assessing the business impact of identified performance risks.

This conclusion is supported by the ISTQB CTAL-TTA syllabus, which outlines the responsibilities and focus areas for Technical Test Analysts, highlighting their involvement in understanding and mitigating technical risks rather than assessing business impacts​​.