n of the dataset is designated to the test sample to evaluate model performance on data the model has not yet seen. **Clean, subset, and handle missing data if necessary** before the splitting process commences.  

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# Model performance

**Performance metrics** are used to see how well a model predicts a specified outcome on training and test datasets.  

A model that performs poorly on the training dataset is **underfit** because it is not able to discern relationships between the `\(x\)` and `\(y\)` va