Case Study

Investigating a gap between training and validation performance in a restaurant review classifier

Case context: You build a sentiment model for restaurant reviews, and it performs very well on the examples used for training. When you test it on a separate development set gathered from another app, the accuracy drops noticeably. This suggests the two datasets may not match well.

Question: What is the first analysis you should perform, based on the recommended troubleshooting approach, to understand this performance gap?

Sample answer: Start by comparing the training data and the development data to find out which characteristics are different. Check for changes in source, wording, label balance, noise, or other data features that could explain the drop.

Key points:

  • A large drop on the development set can signal that the two datasets come from different distributions.
  • The next step is to inspect and compare the data itself instead of adjusting the model blindly.
  • The goal is to identify the specific ways the two datasets do not line up.

Rubric: The learner must say that the next recommended step is to determine which properties differ between the training data and the development data.

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Updated 2026-08-12

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Machine Learning

Deep Learning

Supervised Learning

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Machine Learning Strategy

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