Please Google and find that source.
I appear to have been mistaken and my initial doubt has proven correct. Instead the statistic was that the vast, vast majority interned from Catholic/Nationalist side.
That said, there is plenty of evidence that a significant number of people were interned for no good reason. The excellent CAIN website is a great resource tool for those interested.
CAIN: Events: Internment: Summary of events
cain.ulster.ac.uk
"The policy proved however to be a disastrous mistake....The crucial intelligence on which the success of the operation depended was flawed and many of those arrested had to be subsequently released because they were not involved in any paramilitary activity."
The complaint was mainly that it was being applied very one sidedly, which is of course true, but even that can be justified; loyalists were not a threat to the state
I would have to respectfully disagree with that sentiment. Loyalists may not have been intent on threatening the NI state, but their actions certainly had the effect of destabilizing the very state that they were committed to upholding.