A reader has taken issue with my maths in my article “Should I Become A Driving Instructor?” (which is now updated for 2018, though the following article applies to the 2010 version). He says:
…I have to say your maths is totally to pot.The pass rate figures are for each exam taken.You fail to take account that most canditates wouldn’t (sic) just have only one attempt and then if they fail stop, they will have up to three attempts at each of the exams.
Let me clarify. Yes, the pass rates are for each exam taken. So if the pass rate is 52% for Part 1, it is 52% every time you attempt it. The only improved chance you stand as an individual on retakes is if you revise more, and while I agree that this will possibly change the overall success rate at Part 1 for an individual, the fact remains that the pass rate is 52%. That 52% pass rate includes people taking it time and time again.
Probably the most important thing, though, is that if you fail it because you don’t know the answers then you will probably fail it every time you take it unless you really do some work in between tries. That 52% is a measured pass rate and not a probability! It isn’t like tossing a coin. With the later exams involved in becoming an ADI, the lower pass rates make the situation worse for people who fail badly due to not being up to it.
To make things simpler, imagine you have to pass three exams, and that you can’t take the next one until the one before is passed. Imagine also that the pass rate for each exam is 50% – and that 50% includes every result (retakes as well as first tries). Imagine that 100 people set out to take these exams.
Since only 50% of those taking the first exam will pass first try, only 50 people are eligible to take the second. The other 50 can keep retaking the exam again and again – but if the exam requires absolute knowledge, and isn’t just down to potluck, then those people will not all pass.
Imagine now that the second exam can only be tried three times, and that it also requires absolute knowledge and isn’t just a formality. Let’s assume that after retakes, the original 50 who passed the first exam has increased to… 75 (and that is being very generous when we know that the 50% pass rate includes retakes and that to pass you must attain a high standard of knowledge or some skill). Only 37.5 (say 38) will pass the second exam – but let’s be generous and inflate this to 50 after two retakes. So, 50 people now go on to take the final exam, and only 25 pass – again, let’s be generous and inflate this to 35 after two retakes.
By making a lot of unsubstantiated assumptions and being generous we have achieved an overall pass rate of about 35% – or a failure rate of 65%.
In my post I simply stuck with factual data: the measured pass rates (including retakes). I did not make any assumptions about pass rates on 2nd and third attempts. If we apply that to our 50:50:50 exams, above, then out of 100 people 50 pass the first exam, 25 pass the second, and 12.5 pass the third. So, a pass rate of 12.5% (or failure rate of 87.5%).
A failure rate of 87.5% or 65%… what does it matter? It is a high failure rate! That is the point I was making.
And with 52:42:24 pass rates, whether you like it or not the failure rate can be as high as 95%. Even if you are being generous, it is still going to be well over 70% – but the kind of people trying to become instructors these days does not support too much generosity: the majority are not going to make it.
EDIT 5/1/2011: The latest pass rates for Parts 1, 2, and 3 are 45%, 50%, and 34% respectively. Those are 2010 figures obtained from the DSA (now DVSA, of course) .