Sure you can, random sampling should work. Don't just go making things up.

Of course actually carrying out that experiment would be absurd since I don't think anyone expects an appreciable percentage of clearnet material to be CSAM. The working assumption is that the goal is to find a needle in a haystack so GP's objection about needing to know the false negative rate is misguided.

if you want perfection. But the eu should be doing investigation that they can use statistics to create a good estimate.