First, I was incredibly nervous when it came to it. I am not usually so on-edge when doing speaking gigs; but usually I have a reasonable billing (and thus reasonable time to get a nuanced point across). Another factor was that I knew that I was being asked to defend a position that was potentially very emotive—and, sure enough, they wheeled on some couple whose son had been killed in a drink-driving accident (of which more later).
Second, although I had made extensive notes and had, I believed, a well-structured argument, this was thrown out slightly by that fact that, when the section finally came up, they had changed the question to "should we ban any drinking before driving"? Although I had anticipated this as a counter-argument to some of the points that I might raise, I had not expected to have to kick off defending that position.
Third—and this is what this post will deal with—I was ambushed by figures that I had, quite simply, never heard before. These came, most specifically, from Dr Valerie [someone or other] from the British Medical Association.
The first claim that she made was that, with 80mgs in the blood, reaction time was impaired by 12%. Sensibly, I should have asked "so what is the average reaction time, in milliseconds?" because, when I asked her afterwards, she had absolutely no idea. She waffled about lots of extenuating circumstances, blah, blah, which would probably have satisfied the audience—but her not having the figures would have put her on the back foot—as would the audience understanding that 12% of, say, 10 milliseconds is utterly insignificant.
However, the most important claim that she made was that the risk of being involved in an accident with 80mgs of alcohol in your blood (the current limit) was ten times that of someone with none.
I have found out since that this was, quite simply, a lie.
Again, talking to her afterwards, I challenged her assertion and asked her where she had got her data. Valerie had not, in fact, got the data herself (her researcher had) but the graph that she showed me was this one—and seen exactly as below.
On production of this artifact, the conversation went something like this...
"This came from the World Health Organisation. And... Well, I don't have another graph but I know that this has been replicated all over the place." She stabbed at the graph's y-axis saying, "see, there's 20.00."
"Yes," said I. "But that point at 0.8 is nowhere near ten times the likelihood of crashing."
Having noted some of the details, I have tracked down the WHO paper that it came from—the WHO Drinking And Driving, A Road Safety Manual For Decision-makers And Practitioners. Oh yes? Those discredited IPCC synthesis reports are always described as "for decision-makers"—it usually means that they are rather more political documents than nuanced science.
Anyway, you can find the graph that she was referring to in the section entitled Chapter 1: Why is a drinking and driving programme necessary [PDF, 397kb] which is not a title that fills me with the confidence that this is going to be, in any way, unbiased. For those who cannot be bothered to download the damn thing, here's how the graph appears in situ.
The first thing to understand is that this is a relative crash risk: if you drink no alcohol at all, the risk of crashing is, quite obviously, not zero—otherwise alcohol would be a factor in 100% of road crashes, rather than the 6% (2008) that it actually is.
The second point is that this is the outcome of a number of studies, starting with one in Michigan, US, in 1964, but is the one featured in the most recent of those, from 2002.
In 196 a case-control study was carried out in Michigan in the United States known as the Grand Rapids study (15). It showed that drivers who had consumed alcohol had a much higher risk of involvement in crashes than those with a zero BAC, and that this risk increased rapidly with increasing blood alcohol levels. These results were corroborated and improved upon by studies in the 1980s, 1990s and in 2002 (16–18). These studies provided the basis for setting legal blood alcohol limits and breath content limits in many countries around the world.
The real point to note is the second paragraph of the accompanying explanation... [Emphasis mine.]
The studies found that the relative risk of crash involvement starts to increase significantly at a blood alcohol concentration level of 0.0 g/dl and that at 0.10 g/100 ml the crash risk relative to a zero BAC is approximately 5, while at a BAC of 0.2 g/100 ml the crash risk is more than 1 0 times the risk relative to a zero BAC (see Figure 1.2).
In other words, at 100mgs, the risk of crashing is five times higher than at baseline. Valerie from the BMA was claiming an increase of ten times at 80mgs—which is, to say the least, a little creative.
Or, as I like to call it, a lie.
One of the things that we would obviously like to know is, roughly, what is the baseline? Presumably it is not zero, because five, or even ten, times zero is zero. So, in actual percentages, what is your average chance of crashing when you are sober? If you get in your car and drive somewhere, what is the chance that you will have an accident?
I have had an inordinate amount of trouble trying to quantify this: if I could even find an estimate for the number of road journeys made every year, that would help. If anyone knows where to find such figures, please, let me know.
Otherwise, I shall proceed to try to piece the bits together in my next post...