Essay

Why More Training Data Does Not Fix a Large Training Error

Question: A speech classifier still has a training error much higher than the target error. Explain why collecting more training examples is not the right fix in this situation, and state what the engineer should concentrate on first.

Sample answer: When the training error is high, the main problem is usually high avoidable bias. Adding more training data is useful when the model has high variance, because extra examples can help it generalize better to new data. But if the model already performs poorly on the training set, more data will not make it better at fitting the examples it already has. The right next step is to improve the model's fit on the training set first, before expecting meaningful gains on validation or test performance.

Key points:

  • More training data mainly helps with variance, not with high training error.
  • A large training error relative to the target indicates high avoidable bias.
  • Collecting more data does not substantially reduce bias.
  • The engineer should first improve performance on the training set.

Rubric: Response should explain that adding more data is helpful for variance but not for a model that already has high training error. It must identify the problem as high avoidable bias and state that the engineer should focus on improving training-set performance before expecting better validation or test results.

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Updated 2026-08-12

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