Logistic Regression Bias–Variance in High‑Dimensional Ads Prediction
Scenario
You are building a large‑scale binary classifier (e.g., click/conversion prediction for Google Display ads) with hundreds to thousands of mostly sparse, high‑cardinality features (one‑hot categorials, text/ids, and some numerics). The dataset is large and exhibits class imbalance.
Question
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In this setting, does logistic regression typically underfit or overfit? Describe the conditions that drive each outcome.
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How would you detect underfitting vs overfitting in practice (e.g., learning curves, cross‑validation)?
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What techniques would you use to address each case (consider regularization strength, feature selection, high‑dimensional sparsity, and related tooling)?