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Underfitting

As explained in Machine Learning for Tabular Data: XGBoost, Deep Learning, and AI

Underfitting is a modeling failure in which a model is too simple to capture important patterns in the data.

Underfitting occurs when a model is too simple to capture important patterns in the data. It often appears as weak predictive performance and systematically flat predictions. section 7.2.3

Linear regression baseline

A linear regression baseline for listing prices produced an R-squared of 0.32, MAE above 12,000 Yen, and predictions that departed from the ideal-fit line with a flat trend. Some predictions were negative, although only about 0.5% were nonpositive. These results signal that the baseline misses important structure rather than providing a strong final model. section 7.2.3

Use baseline diagnostics to investigate whether the model is underfitting:

  • Compare cross-validation predictions with expected target values across data subsets. section 7.2.3
  • Inspect feature coefficients and individual case contributions before choosing a more complex model. section 7.4
  • Use the baseline’s limitations to guide tentative choices for nonlinearities, interactions, targets, and hyperparameters. section 7.4

How Machine Learning for Tabular Data: XGBoost, Deep Learning, and AI covers it

How deep it goes
Diagnoses underfitting through cross-validation predictions, metrics, plots, infeasible outputs, and coefficient inspection.
Examples
Uses a listing-price regression baseline, flat prediction plot, negative predictions, error metrics, and case-level coefficient contributions.
What it assumes
Assumes validation strategy, exploratory data analysis, and a prepared data pipeline before model comparison.
What you can do after
Diagnose/debug with cross-validation predictions, evaluation metrics, plots, prediction ranges, and coefficient contributions.
How it connects
Connects underfitting with cross-validation, linear regression, model evaluation, nonlinearities, interactions, and hyperparameter selection.

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This explainer was generated by Manning's knowledge graph from the text of Machine Learning for Tabular Data: XGBoost, Deep Learning, and AI. The section links point to the parts of the book it draws on.