You want a rule. Something in the shape of: if slept under six hours, drop one set.
Write it and you will follow it for four weeks and it will be wrong twice,
and you will have no means of identifying which twice.

The rule is not available. Not because you have read too little —
you have read more than anybody at these racks.
Because the thing you are trying to rule on is one body on one evening,
and there has only ever been one of it, and it has never been randomised against anything.

The Book of the Scholar — Wall 41:4