Would you buy this car?

Imagine the much-respected inspectors doing a survey of car handbrakes and reporting that 30 per cent were inadequate. 

Keep imagining, as another survey by specialist inspectors found that 25 per cent of all gearboxes were ineffective. A further group of inspectors find that a third of the car engines they observed were unsatisfactory. Imagine what you would think if you were then told that general car inspectors had found more than 75 per cent of all cars were good or better.

If the specialists are highlighting significant problems, it seems hard to believe that the overall picture is good. There is either something wrong with the data, the inspectors or the process. We would probably be very tentative about driving a car described as good for fear that some serious inadequacies lurked beneath the surface – even though the individual car had the official quality mark.