It depends on which group of offenders you're looking at. It's highly dependent on the characteristics of the individual offenders. Offenders who are high risk may be returned to custody at a rate as high as 50% for violating a condition, whereas low-risk offenders may be returned at a rate of about 20% for violating a condition over an extended period of time.
On March 1st, 2012. See this statement in context.