Debug a model with class imbalance

Last updated: December 3, 2025

Quick Overview

Your model shows high variance. Walk through your debugging process and potential fixes.

Shopify
Machine Learning
Machine Learning Engineer
Shopify
December 3, 2025
Machine Learning Engineer
Phone Screen
Machine Learning
Medium

263

7

400 solved


Your model shows high variance. Walk through your debugging process and potential fixes.

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

What the Interviewer Expects
  • Explain the mathematical foundations with clarity
  • Discuss practical implementation considerations and hyperparameter tuning
  • Analyze the technique's strengths and weaknesses for different data types
  • Demonstrate understanding of evaluation methodology and metrics
  • Connect theory to real-world applications with concrete examples
Key Topics to Cover
Class imbalance handling
Ensemble methods (bagging, boosting, stacking)
Gradient descent and optimization
Overfitting and underfitting
Feature importance and selection
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 handle a highly imbalanced dataset?
  • 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 Explanation

Start with a clear, intuitive explanation of the concept. Use analogies when helpful. Then go deeper into the mathematical foundations: **Key Intuiti...

Practical Application

**When to use**: Describe the scenarios where this technique is most effective. What data characteristics favor it? **When NOT to use**: Common pitfa...


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