A community-choir attendance model looks excellent because the same holiday-concert weekends were used both to fit it and to announce its score. The director wants a number that estimates how it will do on future weekends it has not seen. What should the team do?
Select an answer to reveal the explanation.
Short Explanation
Think of practicing the same concert and then calling that rehearsal the review. Hold out weekends the fitting step never saw, or the published score is just a trophy. Shrinking the spreadsheet or rescoring the holiday rows does not simulate next season.
Full Explanation
Train, validation, and test splits exist so the published score is an unbiased estimate of future performance. Fitting and announcing a score on the same holiday weekends inflates that number. Making a file smaller is not the purpose of a split, and scoring the training rows again does not simulate new weekends. Spreadsheet storage does not remove the need for held-out data.