Debug a model with class imbalance

Last updated: August 6, 2025

Quick Overview

Your model shows poor recall. Walk through your debugging process and potential fixes.

SpaceX
Machine Learning
Machine Learning Engineer
SpaceX
August 6, 2025
Machine Learning Engineer
Technical Screen
Machine Learning
Easy

196

6

1,183 solved


Your model shows poor recall. Walk through your debugging process and potential fixes.

Machine learning questions at SpaceX test both theoretical understanding and practical experience. This Technical Screen question evaluates your knowledge of ML fundamentals and your ability to apply them to real-world problems.

What the Interviewer Expects
  • Explain the concept clearly with intuitive examples
  • Discuss when and why to use this technique
  • Identify common pitfalls and how to avoid them
  • Compare with alternative approaches at a high level
Key Topics to Cover
Overfitting and underfitting
Cross-validation and model evaluation
Feature importance and selection
Bias-variance trade-off
Supervised vs unsupervised learning
Regularization techniques (L1, L2, dropout)
How to Approach This
  1. Understand the bias-variance trade-off. High training accuracy but low test accuracy signals overfitting.
  2. Choose evaluation metrics carefully based on the problem. Accuracy alone is often insufficient.
  3. Feature engineering is often more impactful than model selection.
  4. Know when to use tree-based models (tabular data) vs neural networks (unstructured data).
  5. Handle class imbalance with SMOTE, class weights, or appropriate loss functions.
Possible Follow-up Questions
  • How would you detect and handle concept drift?
  • How would you explain this model's predictions to a non-technical stakeholder?
  • When would you prefer a simpler model over a complex one?
  • How would you ensure reproducibility in your ML pipeline?
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Sample Answer
Core Concept: Class Imbalance in Machine Learning

Class imbalance occurs when the distribution of classes in the target variable is not uniform, leading to some classes being underrepresented. In the context of SpaceX, this could manifest in predicti...

How It Works: Techniques to Address Class Imbalance

To debug poor recall due to class imbalance, I would first analyze the data distribution. Techniques to mitigate this imbalance include:

  1. Resampling Techniques: Oversampling the minority class (...

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