The original claim—press released around the world this week—stated that:
There is evidence to suggest that the levels of SHS present in vehicles can contribute to a serious health hazard for adults and children. Further studies demonstrate that the concentration of toxins in a smoke-filled vehicle is 23 times greater than that of a smoky bar, even under realistic ventilation conditions.
In the studies a number of ventilation conditions were assessed, where airflow parameters included average driving speed, presence of air conditioning and open windows. Realistic ventilation is described as driving at average roads speeds with all four windows completely open.
The BMA has now rewritten their briefing paper (the previous version has now disappeared) so that it now reads:
There is evidence to suggest that the levels of SHS present in vehicles can contribute to a serious health hazard for adults and children. Further studies demonstrate that the concentration of toxins in a smoke-filled vehicle could be up to 11 times greater than that of a smoky bar.
In the studies a number of ventilation conditions were assessed, where airflow parameters included average driving speed, presence of air conditioning and open windows.
Aside from removing the now-notoriously fictitious "23 times" claim, it is significant that the BMA has removed all reference to "realistic conditions". As I have said before, when experiments have been conducted in realistic conditions (ie. with one or more windows at least partially open), the amount of secondhand smoke in a moving vehicle is much lower than in a smoky bar. When all windows are closed and the ventilation is turned off, however, concentrations are higher than in a smoky bar. Of course they are. Cars are smaller than bars. That's why people who smoke in a car open the window.
The BMA's half-correction is welcome. I wonder if they will use their formidable PR machine to make sure the media get the message? (Rhetorical question). The fact remains that millions of people have now been informed that secondhand smoke in a car under realistic conditions "is 23 times" more concentrated than secondhand smoke in a bar.
Now, with the world's media having moved on, the BMA has little to lose by quietly announcing that what they meant to say was that secondhand smoke in a car under unrealistic conditions "could be up to 11 times" more concentrated than secondhand smoke in a smoky bar.
Perhaps the BMA should launch a campaign to make people smoke under realistic conditions?
I'm grateful to Ivan who has left a comment leading me to this interview from the Today programme with Dr Vivienne Nathanson, the head of science and ethics at the BMA. The fact that she wants it to be illegal for people to smoke in their own car demonstrates her weak grasp of ethics. This interview demonstrates her weak grasp of science.
Bear in mind that this immediately followed an interview with Simon Clark who mentioned the debunking of the "23 times" claim in the Canadian Medical Association Journal.
Interviewer: What is the evidence?Pretty emphatic stuff, there. Of course, what the peer-reviewed study actually says is...
Nathanson: Well, the evidence is, in fact, that the levels of toxins that can build up in a car do reach 23 times the levels in a smoky bar...
Interviewer: And that is—sorry to interrupt you—but that is peer-reviewed?
Nathanson: Yes, absolutely.
Interviewer: Everyone in the scientific community accepts that it's true?
We recommend that researchers and organizations stop using the 23 times more toxic factoid because there appears to be no evidence for it in the scientific literature.
It's also worth reading this blog post which casts a critical eye on some of the other claims in the BMA's latest report.