Essay

Why training data and evaluation data may come from different sources

Question: In a concise analytical response, explain why a dog detector might be trained with a mix of labeled web photos and storefront-camera images, while dev and test sets use only storefront-camera images.

Sample answer: The web photos can enlarge the training set and give the model more examples to learn from, which is helpful when labeled data are limited. However, the system will be deployed on storefront-camera images, so dev and test sets should match that future operating environment. Using storefront-camera data for evaluation makes the measured performance more relevant to the real task, even if the training data include additional sources. For that reason, the training distribution and the dev/test distribution can intentionally be different.

Key points:

  • Web photos increase the amount of training data.
  • Storefront-camera images match the deployment setting.
  • Dev and test sets should reflect the data the model will face in production.
  • Different distributions can be chosen on purpose when they serve different roles.

Rubric: A strong response explains that extra web photos help the model learn, states that storefront-camera images are the target distribution, ties dev/test selection to realistic evaluation, and notes that the training and evaluation distributions may differ by design.

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Updated 2026-08-12

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