I over-stated the evidence. I was thinking of a study claiming 85% of felons convicted of child porn possession also admitted to also committing child sexual abuse in anonymous reporting. But it seems there's a lot of controversy around that study: https://www.nytimes.com/2007/07/19/us/19sex.html .

That said, my understanding is the evidence does seem to indicate a correlation between the two, though in the 30-40% range. See https://web.archive.org/web/20080111204617/http://www.ndaa.o... for example. Not a majority, but still significant. And, of course, this sample is just people who were convicted of possession, not all people who ever viewed such material, so I'd have to qualify my statement to "convicted consumers of child porn"

I agree with this post. Lots of people viewing images of child sexual abuse will go on to commit a contact offence (or already have committed a contact offence).

But there are plenty of people who won't go on to commit a contact offence.

This is a problem for law enforcement because they need to monitor all people who've viewed images of child sexual abuse in order to stop them committing contact offences, and this second group inflates the numbers. Maybe it's only 20% more, but maybe it more than doubles the numbers.