How Not To Understand Statistics

We’ve not had one of these for a while, but another association is getting itself all Statisticsconfused over pass rates.

On the blog I’ve linked to pass rates for all UK test centres between April 2010 and February 2011. These are intended as a guide, and they will change slightly with time. During the period covered, Bradford’s two test centres had pass rates of 30.7% and 29.4%, compared to the National Average at the same time of 46.4%.

The article here is going on about the pass rates at Bradford’s two centres between April and August 2011 – presumably someone showing how clever they are by requesting the data under FOI – which were 30.1% (down insignificantly on my data by 0.6%) and 35% (up significantly by more than 5%) respectively.

A local “leading driving instructor” appears to be claiming that test fails are guaranteed at certain times of day…

…due to poor parking by other motorists at junctions.

The local association says:

Certain routes are such, at particular times, that even a good driver has difficulty getting out of a junction because cars are parked so close to corners, they are bound to fail at those times.

The same spokesman adds:

I could take a pupil to another test centre in another area and they would pass.

How many times have I heard that! How many of my pupils have failed “because of someone else” over the years? However, another spokesman from the same organisation says:

…congestion experienced along the Heaton test route was also to blame for the high failure rate, as well as poor preparation by some candidates .

I think that last thing is getting a little closer to the real reason for overall low pass rates.

Hasn’t anyone drawn the obvious conclusion here that the pass rate is lower than most other places because of the quality of the candidates? And that the standard of parking these people are complaining about is simply an example of a vicious circle – anyone who passes is likely to end up behaving in exactly the same way?

I’ve mentioned this before, but if you look for the highest pass rate – for Mallaig, in Scotland (Google Map it) – you will see that it has less than a dozen roads and only two of them join in such a way that you could avoid having to perform a turn in the road somewhere. I reckon that the total length of roads there must amount to less than 10km. The pass rate is over 70%, and I’m certain that many of mine who fail first time here could well pass first time up there – but I can’t prove that or do anything about validating it… because I don’t live there! And nor do those test candidates in Bradford.

Now, I won’t explain this in any greater detail, but Bradford is NOT the same as Mallaig. Nor is it alone in having “tricky” roads or idiot members of the public to deal with. Most cities have those.

That second spokesman adds:

Parked cars, inconsiderate road users – new drivers are not prepared for these circumstances.

They bloody well should be prepared – that’s what we get paid for! The bottom line is that you have to prepare your pupils for whatever they are going to have to cope with both on the test and in real life. You can’t start whingeing about them failing just because they’re not good enough to pass.

By all means try and get people to park better. But don’t blame test failures for it, when the people you’re teaching are going to behave in exactly the same way the second they pass.

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