Question: In a concise analytical response, explain why repeatedly examining one portion can cause overfitting and how keeping another portion hands-off helps reveal it.

Sample answer: Repeated manual inspection lets development decisions become increasingly tailored to the examined portion, so that portion is overfit more rapidly. By explicitly reserving another portion that is not manually examined, developers retain a separate basis for parameter tuning. Differences between results on the examined and unexamined portions can indicate that manual error analysis is causing overfitting to the examined data.

Key points:

• The manually examined portion is overfit more rapidly.
• The other portion is not manually examined.
• The unexamined portion can be used for parameter tuning.
• The explicit split helps reveal overfitting caused by manual error analysis.

Rubric: A strong response identifies the greater overfitting risk for the examined portion, explains the role of the hands-off portion, and connects the explicit split to detecting overfitting caused by manual error analysis.