Many a time when rape is discussed, a major arguement in one form or another will be that the majority of rapes are not reported and thus the amount of rapes committed must be astronomically higher.

This begets the question: How do you (collectively every using this arguement) know about these unreported rapes? Doesn't the fact that they are unreported mean that we should not know about them? I can only figure that through anonymous surveys this information has come to light, but how can one trust something like this?

In short, where does the information come from that states how many rapes are unreported.