Short Answer

Why must dev and test sets share the same distribution to clearly diagnose dev set overfitting?

Question: In one to three sentences, explain why dev and test sets must come from the same distribution for a dev/test performance gap to clearly indicate dev set overfitting.

Sample answer: If dev and test sets come from the same distribution, any performance gap cannot be blamed on the test data being different, leaving dev set overfitting as the clear explanation. If the distributions differed, the gap could instead be due to the test set representing different data, making the diagnosis unclear.

Key points:

  • Same distribution removes distribution mismatch as a competing explanation
  • This isolates dev set overfitting as the clear diagnosis

Rubric: Answer should note that shared distribution eliminates distribution mismatch as an alternative explanation, isolating overfitting as the cause.

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Updated 2026-07-11

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