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Getting Older Drivers And Breath Tests, Drunk Driving, Entirely Wrong

In order to understand what a statistic is telling us we’ve got to grasp how those numbers were constructed. So it is with this report on older drivers, breath tests and drink driving. It’s possible to discern the truth here as long as you understand one rather important fact. England does not allow random breath testing to check for drunk driving. Once we’ve got that much of what is being wurbled about goes away.

For example:

[perfectpullquote align=”full” bordertop=”false” cite=”” link=”” color=”” class=”” size=””]While much media attention is paid to younger drink drivers, with those aged 20-34 accounting for more than half of all failed breathalyser tests in Great Britain, very little attention is paid to older drink drivers, who account for one in seven (15 per cent) failed breath tests.[/perfectpullquote]

No, our numbers don’t mean that at all.

[perfectpullquote align=”full” bordertop=”false” cite=”” link=”” color=”” class=”” size=””] More than 1.6 million motorists over the age of 55 have driven while over the limit, a study suggests. Research by Direct Line Motor Insurance also found that the problem could be more widespread, with a further 3.6 million drivers in the age group admitting they thought they could have been over the limit while behind the wheel. [/perfectpullquote]

As lifetime numbers for having driven 500 yards after a second pint that’s not too bad really.

[perfectpullquote align=”full” bordertop=”false” cite=”” link=”” color=”” class=”” size=””]There also appeared to be a worrying lack of understanding about the effect of alcohol with more than two-thirds believing that men can drink more than women and be safe to drive, when in reality it is down to a variety of factors such as, but not limited to weight, medications and diet.[/perfectpullquote]

The folk wisdom is actually correct as a general rule of thumb. Men tend to be heavier than women thus they can indeed drink more. And it’s not really weight either, it’s blood volume – you know, dilution of booze when in the bloodstream?

But back to the lessons that will be learned from this. We do have to note that English police aren’t allowed to just test any- and every- one. Random testing is illegal. They must have what the Americans call probable cause to be able to stop someone to ask for a breath test. Thus our numbers of those who fail such tests are not some estimation of any general drink driving rate. They’re a measure of those observed to have behaviour likely to have been caused by booze whose behaviour has been caused by booze. And thus they’re not extensible to the general population in the slightest.

By analogy, we’re measuring here those spotted climbing out of some stranger’s window who turn out, on examination, to be burglars. Not the general incidence of burglary in the country.

As ever in discussing the booze driving statistics it’s worth pointing out that Britain has one of the lowest levels in the world of actual harm being caused by booze driving. Our current mixture of a high-ish limit – by international standards – with only for cause testing plus severe penalties upon conviction seems to work rather well. It ain’t broke so don’t fix it.

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