A harmless-looking column that reveals the result

A worked example using a hypothetical scenario to show how the reasoning applies.

The scenario

A hypothetical dataset includes a trainer form measure recalculated after every meeting. Using its present value for a prediction made months earlier includes later races. A historical snapshot or a correctly reconstructed as-of value is needed. Renaming the column does not fix the information leak.

What to take from it

Ask when a value became knowable, not only whether it has a plausible racing explanation.

What to check next

• Attach an availability timestamp to each input.
• Split the evaluation in a way that matches the intended deployment.
• Rebuild features using only information available at the cutoff.

Keep the conclusion specific

Separate the observation, the interpretation and the unresolved question. A worksheet is most useful when its conclusion stays within the evidence entered into it.

The checklist does not certify a dataset or claim access to the PTPTips model.