AA study causes drug headlines
Journalists are often reluctant to attribute causes for individual events — the journalistic use of ‘after’ and ‘amid’ leads readers to conclusions in a much more deniable way — but less reluctant for groups.
Today, there’s an interesting range of descriptions of some research
Herald: Automobile Association study finds drugs cause more fatal crashes than alcohol
Stuff: Drug-impaired drivers now involved in more fatal crashes than drink-drivers
Radio NZ: Drugged driving fatalities outnumber drink driving deaths
NZ Autocar: AA FINDS MARKED INCREASE IN DRUG DRIVING FATALITIES
None of these link to the actual study report, and when I first looked, the report was on the AA website or on Scoop, but it the results table is in the NZ Autocar story. (Scoop has a press release from 10:49am; it’s still not on the AA website, where the most recent media release is dated 21 May)
None of the headlines is supported all that well by the data.
The data are based on what’s recorded in the ‘Crash Analysis System’, and is based on blood alcohol above the legal level and on presence of illegal drugs or prescription drugs that might have impaired the driver. It’s not based on actual impairment (which is obviously hard to measure after the crash). The Crash Analysis System is set up to record anything that might be a contributing cause, because if some factor doesn’t make it into the database there’s no way to go back and check it later. Back in 2015 when the data were public and I looked at them, the system averaged about 2 1/4 causes per crash.
We pretty much know that most crashes where the driver is not far above the legal blood alcohol limit are not caused by alcohol — that’s the whole point of setting the threshold where it is. For some illegal drugs — notably, cannabis — there isn’t a good test for impairment in regular users.
The AA says that other countries are using roadside testing. They are, and that’s partly because some countries regard the false positives — catching someone who has used illegal drugs but isn’t impaired at the time — as a feature, not a bug. The combination of alcohol and cannabis does seem to be a real problem, and US expert Mark Kleiman has suggested a blood alcohol threshold of zero for people who use cannabis.
But on top of that, as the NZ Autocar story says
While the numbers suggest drug driving has suddenly skyrocketed, the AA believes the big jump is likely down to more thorough testing being done following crashes.
That’s also in the press release. But it’s not in the other stories.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
How do we get the raw data?
7 years ago
You need to apply for access. The webpage is here, and it’s got an email address for enquiries.
7 years ago
Firstly, I think anyone with a rudimentary understanding of substances and impairment would question these claims.
I google dug for 5-10min, using colorado as my search.
This link had some quality stats
https://www.criminallawdenver.com/drugs/drugged-driving-statistics/
However, when one factors in levels of policing as evident by these NZ stats…
https://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=12058539
….the objectivity of any data starts to become blurred. The herald link above shows a worsening NZ [esp auckland]accident trend not seen elsewhere in the world, where drug use is rising by similar levels….
The previously used negative dialogue of schizophrenia and psychosis among cannabis users, has been debunked, as the skyrocketing use of cannabis since the 60’s, schizophrenia stats have remained static. Indeed, cannabis appears to be one of the best antipsychotics available.
Doctors recommend camels…
7 years ago
(note that some posts end up needing human moderation before they appear)
7 years ago
As well, synthetic cannabis results may be lumbered in with natural cannabis, further inhibiting any chance of true understanding around impairment and drug use in NZ.
7 years ago
I made a lengthy post of info I had gathered but it didnt load, cant be bothered doing it again so here is a link from Colorado
https://www.criminallawdenver.com/drugs/drugged-driving-statistics/
7 years ago
Its anecdotal, but a mate of a mate who attended ‘The Daktory’ for years observed certain users imbibe heroic and unbelievable amounts of cannabis [some users powered through 3g of high thc buds over a 5 hour period] and drive home afterward, night after night after night, for years, with no accidents. This level of consumption would be like having 50plus units of alcohol or more….
Another who dosed much lower, had improved his pool playing skills to a masterful level.
This venue had banned alcohol altogether, few used it at all, and caffeine use was very limited.
As well, doctors recommends amphetamine meds for focus and concentration, so even meth use may in fact improve concentration at the wheel.
7 years ago