While I'm not sure I've yet got my head completely around the
statistical methods here the claim is that the design of the study
caused the drivers to act as their own control group thus isolating cell
phone use from other factors. Quoting from the paper:
Methods
We used a case-crossover design, a variation of a case-control
design that is appropriate when a brief exposure (driver’s phone
use) causes a transient rise in the risk of a rare outcome (a crash).
We compared a driver’s use of a mobile phone at the estimated
time of a crash with the same driver’s use during another suitable
time period. Because drivers are their own controls, the design
controls for characteristics of the driver that may affect the risk of
a crash but do not change over a short period of time. As it is
important that risks during control periods and crash trips are
similar, we compared phone activity during the hazard interval
(time immediately before the crash) with phone activity during
control intervals (equivalent times during which participants
were driving but did not crash) in the previous week.
The original paper is at the British Medical Journal and can be found here:
<http://bmj.bmjjournals.com/cgi/rapidpdf/bmj.38537.397512.55v1?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&author1=McCartt&fulltext=cell+phone&andorexactfulltext=and&searchid=1121377498478_13934&stored_search=&FIRSTINDEX=0&sortspec=relevance&resourcetype=1>
And for those important statistical nums see the abstract here:
<http://bmj.bmjjournals.com/cgi/content/abstract/bmj.38537.397512.55v1?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&author1=McCartt&fulltext=cell+phone&andorexactfulltext=and&searchid=1121377498478_13934&stored_search=&FIRSTINDEX=0&sortspec=relevance&resourcetype=1>
which says:
Design: A case-crossover study.
Setting: Perth, Western Australia.
Participants: 456 drivers aged 17 years who owned or used mobile phones
and had been involved in road crashes necessitating hospital attendance
between April 2002 and July 2004.
Main outcome measure: Driver's use of mobile phone at estimated time of
crash and on trips at the same time of day in the week before the crash.
Interviews with drivers in hospital and phone company's records of phone
use.
Results: Driver's use of a mobile phone up to 10 minutes before a crash
was associated with a fourfold increased likelihood of crashing (odds
ratio 4.1, 95% confidence interval 2.2 to 7.7, P<0.001). Risk was raised
irrespective of whether or not a hands-free device was used (hands-free:
3.8, 1.8 to 8.0, P<0.001; hand held: 4.9, 1.6 to 15.5, P=0.003).
Increased risk was similar in men and women and in drivers aged 30 and
<30 years. A third (n=21) of calls before crashes and on trips during
the previous week were reportedly on hand held phones.
Conclusions: When drivers use a mobile phone there is an increased
likelihood of a crash resulting in injury. Using a hands-free phone is
not any safer.
Enjoy,
Chuck Norcutt
Moose wrote:
> Gary Holder (c) wrote:
>
>
>>Maybe so, but these figures don't prove it. Acxtually, I'm sure they do not
>>rise to "probable". I agree it is NOT smart to use phone while driving and
>>do not myself.
>>
>>
>
> And here you raise the issue of association vs. causality. It is
> entirely possible that personality traits and habitual ways of acting in
> the world of those who tend to use cell phones while driving are also
> those of people who tend to get into automobile accidents, whether using
> cell phones at the time or not. Observation of the world around me
> supports this thesis in my mind.
>
> Since observation, experience and common sense lead me to believe that
> using a cell phone while driving does lead to less attention available
> for driving, I suspect that the actual statistics are an undefined
> mixture of at least those two factors, which will never be separable in
> any statistically meaningful way.
>
> The common, unstated, assumption of popular media and what appears to be
> a large majority of the public that association means causality is
> nonetheless logically and statistically unsupportable.
>
> Moose
>
>
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