MOT failure rates

[rov1200]

http://news.bbc.co.uk.../business/8456116.stm

Why is Ford at the top of the list (% wise) when it comes to MOT failures? These are vehicles said to be taking their first MOT and we are not talking about bangers. A list has been published because of the freedom of information and is no longer secret. With all the resources that Ford possess you would think reliability should be a priority, wouldn't you?

[jake-the-peg]

You've got to look at the data to see if it's meaningful.

Perhaps 90% of the failures were worn tyres and brakes - that'd hardly be Ford's fault would it?

Then when you've adjusted for that you need to ask whether Ford's higher figures are statistically significant or whether that's just this year.

I'm afraid I simply don't have time to crunch the numbers to answer that but I'd guess that there are probably a few poor performers and that Ford is probably not really much different from them.

I guess there are relatively few new car buyers that worry about medium term maintenance when buying a car which is why it happens.

[jno]

maybe Ford is the preferred car for boy racers or white van men, who thrash them to death? Well, that's only a hypothesis, but it's an example of how it might not be anything to do with the vehicles, only with the drivers.

[buildersmate]

Ford still retains its position as the largest market share of new cars registered - 16% in 2009 with Vauxhall next at about 12%. It was in 1st place 3 years ago as well.
It therefore stands to reason that the largest number of cars being MOT tested as 3-year olds are Fords. And, if Fords are equally as reliable as any other brand, it's blindingly obvious that they will also be top of the list of numbers of failures, by percentage. They'd have to be notably better than average to simply avoid being top of the list.
With all the resources that Rov possesses you would think thinking through the logic of the question would be a priority, wouldn't you?

[ABerrant]

buildersmate - the percentage failure rate is per model therefore the market share is irrelevant, e.g.

2004 Ford Transit Connect - 22,900 MOTs - 7,000 failures (30.5%)
2004 Peugeot 307 - 37,300 MOTs - 9,200 failures (24.7%)

[buildersmate]

Fair comment - the link didn't work when I tried it repeatedly (it does now) so I got info from the SMMT.

[rov1200]

Thanks Aberant you utter my sentiments. Of course Ford overall will have more failures because they have more vehicles on the road. Obviously Buildersmate never got beyond his GCSE in maths as he would have spotted the '%' in the question.

Jake worn out tyres etc would apply to all drivers unless for some obscure reason they are doing more miles than everyone else.

[burnhal]

I spotted your % in your question and probably like buildersmate assumed that with no other indication in your statement it meant % of all MOTs. Have another look at your statement!!!!
However- following the link......the 2004 transit connect failures were some 6000 odd. 212 body and structure, over 2000 brakes and well over 2000 drivers view of the road.......... anyone care to expand on what a failure regarding drivers view of the road might mean????

[ABerrant]

Drivers view of the road = Windscreen damage and maintenance.

Possible failures -
wipers (insecure, missing, defective)
washers
cracks
concentrated scratches
grooves
etc.

[burnhal]

so in fact then the data really doesnt mean much in regard to reliabiity of the vehicles!!

[ABerrant]

The data will only be indicative of 'reliability' if you limit yourself the those data sets you wish to define as related to 'reliability' and disregard the rest.

Also, do not be misled into thinking the 6000-odd vehicle failures were comprised of the same number of individual defects. The detailed figures include "advisories" and many vehicles would have failed on multiple defects.

E.g. the 22,925 Transits presented for test (of which 6,987 failed) accumulated 16,614 defects of which 207 were Body & Structure, 2,113 Brakes and 2,512 View of Road etc.

[alfa_male]

You have to be very careful with data like this. The summary table on the BBC is particularly misleading. It looks like the top 12 worst vehicles but it isn't. The list of models has been pre-filtered to only include "Popular" models. So the VW Passat for instance with a fail rate of 19.8% doesn't make the list. Neither does the BMW 3-series which is considered a different model for each engine size (unlike most cars). Add together ALL 3 Series models and you get 37300 tests with 18.5% failure - very similar set of stats as the Vauxhall Zafira.

[S_C]

another reason these figures maybe misleading is the conditions the vehicles have had over there so far short running lives , millage if the owners were careful or good , if they actualy took care of their vehicles or just used them as work horses " so many company car users do this " .
there are so many factors that can add to making a vehicle untest worthy , that the manufacturer cannot guard against , the main one being the owner / driver and how they look after their vehicles

[R1Geezer]

This is an example of statistical accuracy giving no useful information. Someone had to top the list but it was vauxhall a few years ago and no doubt others before that. If I take a note of the colour of the underpants worn by all drivers who crashed their car last year, not doubt a particular colour will emerge as most popular. Would I then be correct in suggesting that wearing that colour underpants is more likely to cause an accident? ........think it through!

[jake-the-peg]

Disagree Geezer

There is probabaly good significant data here but getting it out is a job for a competant statistician not a journalist.

I dont think the fact that Ford is at the top is necessarilly significant but I suspect that the fact that there is a wide disparity between makes probably is.

Drawing those exact distinctions is, however, decidedly non trivial