Well that paper says this:
"Once a compound has been granted orphan designation, the odds for approval are high (82%) compared to traditional drugs (35%)"
I dug a little deeper. The original supplier of this info seems to be this: Bernstein Research. The long view: doing well by doing good – the advantages of adopting a family of orphans. Global Biotechnology, 28 April 2010.
I can't find the Bernstein paper online. But someone else quoted the same research and said this:
"Orphan designations have better odds for approval with an 82% success rate (Phase 2 forward) as opposed to 35% for traditional drugs"
And another online footnoted the Bernstein research as well:
"To date, the failure rate in the orphan drug space has been muted; indeed, Sanford C. Bernstein analysts note an average 82 percent success rate (versus a typical 65 percent success rate for products in Phase III development"
It's not clear and I can't find the source so I'm not taking it too seriously. I'd love to see a chart of orphan designated drugs and their advancement rates through the phases...if anyone has seen one :)