Who are you and why are you presenting? If you're representing the AFCO, they should arm you with some up to date stats. If you're currently serving - brilliant, if only more would give some of their time to provide such opportunities? But still, speak to the AFCO or OASC.
Anyhow, it's good that you're there and the following might help:
About 19% of pilot applicants pass the required aptitude tests but thereafter its a numbers game based simply on demand and supply. If the doors are very open, around 25% of those attending OASC could get selected to IOT.
After that is flying training which, based on recent evidence, has around a 90% success rate from EFT to front line.
All that said, if you're talking to ATC what they must understand is that an increasing number of pilot applications are received from those currently serving in the ranks; that performance at CBAT peaks at around 22 years of age; and that many of the attributes sought at OASC can be improved through some 'time in'. In other words, if you want to be a pilot, but don't pass CBAT first time, then unless you have a better plan (e.g. university)... don't be afraid to join anyway... get stuck in and enjoy yourself... then take the CBAT again in 12 months time (if that's still what you want)!