Sean Rehaag, from Toronto, actually did a study on the subject. I don't have the exact percentages he arrived at, but he found that there was a considerable difference in the success rates of cases where people have representation and those where they do not. I will also tell you that refugee claimants who are not represented do not know how to make their claim. They do not know what evidence to provide, and that means a lot of wasted time for the tribunal.
On February 9th, 2017. See this statement in context.