Point72·Data Scientist·Technical Phone Screen
- How does a CART decision tree choose splits differently for classification versus regression? Walk through the exact formulas for Gini impurity, entropy, and MSE, and explain how surrogate splits handle missing feature values.
- Walk through a defensible procedure for choosing max_depth and min_samples_split, including a cross-validation plan, cost-complexity pruning via the alpha path, and which metric you'd optimize under severe class imbalance and why.
- What are at least three diagnostics you'd use to detect overfitting in a decision tree, and what specific patterns in those diagnostics would flag a problem?
- With 500k rows and around 300 features including high-cardinality categoricals and sparse indicators, how would you preprocess and train a single decision tree? Cover encoding choices, rare category handling, feature binning, any monotonic constraints, and give rough hyperparameter ranges and expected training time.
- Under what data or target conditions would a random forest or gradient-boosted model outperform a single decision tree? Name at least three, and discuss the trade-offs around variance, interpretability, latency, calibration, and how you'd compare the models fairly.
“I knew Gini and entropy cold but surrogate splits caught me mid-sentence.”