03 · Practise and check
Try this yourself
Explain why randomly splitting multiple messages from the same person can overestimate performance on entirely new people.
Check your understanding
The model may learn person-specific patterns shared across splits. A group-based split better tests generalisation to new people.
A mistake to avoid
Do not repeatedly tune choices against the final test score. That gradually turns the test set into another validation set.
Before looking at the answer, write a short explanation and one example of your own. Finish by naming one limitation of the method. Use Mark as read when you are ready, or return to the previous lesson if a term is unclear.
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