03 · Practise and check
Try this yourself
Add an impossible value of -3 study hours. Explain why it needs investigation rather than blindly replacing it with the average.
Check your understanding
Missingness and invalid values are different problems. A missing entry may be unknown, while a negative duration may indicate a recording error.
A mistake to avoid
Do not infer that study hours cause higher scores from this tiny synthetic table. It illustrates inspection, not a causal finding.
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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