How do I approach Machine Learning interview questions?

Machine Learning questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master machine learning interviews.

What difficulty level is this interview question?

This is a easy difficulty Machine Learning question, commonly asked during Technical Screen rounds at LinkedIn.

What role is this question designed for?

This question is commonly asked for Data Scientist candidates at LinkedIn during technical interviews.

Handle imbalance, validate samples, and avoid overfitting

Quick Overview

This question evaluates competencies in handling class imbalance, choosing and interpreting evaluation metrics and decision thresholds, validating sample representativeness and model generalization from very large datasets, mitigating overfitting in decision-tree and ensemble models, and understanding how L1/L2 regularization introduces bias, all within the Machine Learning domain for Data Scientist roles. It is commonly asked to assess both practical application skills—such as model validation, sampling and hyperparameter controls—and conceptual understanding of bias–variance and regularization trade-offs, indicating readiness for production-grade supervised learning problems.

Answer the following applied ML questions.

1) Class imbalance

You’re building a binary classifier where positives are rare.

What are practical ways to handle class imbalance?
Which evaluation metrics would you use and why (e.g., precision/recall/F1, ROC-AUC, PR-AUC)?
How would you pick a decision threshold?

2) Training on a sample from a huge dataset

You have an extremely large dataset, so you train on a sample.

How do you verify the sampled dataset is representative of the full dataset?
How do you verify that a model trained on the sample will generalize to the full distribution?

3) Prevent overfitting in tree-based models

For decision trees / gradient-boosted trees / random forests:

What are the main knobs/strategies to reduce overfitting?
What validation approach would you use?

4) Why aren’t L1/L2 regularized estimators unbiased?

Explain why adding L1 (lasso) or L2 (ridge) regularization introduces bias, and why it can still improve generalization.