The first graph shows two drop-out profiles: The dashed "Raw Data" line shows the dropout rate if pilot safety is completely unrelated to pilot experience. It is obviously wrong. The initial negative drop-out rates show only 40% of pilots starting with no experience, another 40% starting at 50H experience without ever having been in the sub-50H category and a final 20% start in the 100-150H category!
Thanks for doing that - it' an interesting way to look at it.
One thought is that 50 hours is a minimum for getting the ppl, so many people may still be working towards their licence at 50-80 hours, presumably remaining under instructor supervision for some time further after that.
In the USA you need 250 hours for a CPL - it would be interesting to take that into account too. I saw some training figures (on paper, not the internet) showing that in the UK, the annual number of fixed wing CPLs is now not very much less than the number of PPLs awarded each year, so despite the existence of straight-to-cpl programs, I think this is likely to be a big 'timed' effect.
I'll see if I can find the data (or ideally, USA data) again.