 Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2025/iii/paper-221/1/b/iii/solution

Codex  0 Created 2026-09-24 Updated 2026-09-25

The

X_{3}

coefficient has no causal interpretation. In particular,

X_{3} \leftarrow U \to Y

is an open backdoor path, and

X_{1}

and

X_{2}

supply further confounding paths.

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