Mobiles and car crashes: if there’s a link why don’t crashes go up when phone usage does?

I’d like to know what’s wrong with all the studies using different methodologies that find a link. Intuitively I find that using a hand held in a car is distracting at least when I’m dialling. It’s all in the paper from the looks of it, but I won’t get round to reading it and satisfying my curiosity for a while yet. If any Troppodillians get the bug, you can download the pdf file here and if you write it up in comments, you can do all of us curious people a favour.

And the abstract is below the fold.

The link between cell phone use while driving and crash risk has in recent years become an area of active research. The most notable of the over 125 studies has concluded that cell phones produce a four-fold increase in relative crash riskcomparable to that produced by illicit levels of alcohol. In response, policy makers in fourteen states have either partially or fully restricted driver cell phone use. We investigate the causal link between cellular usage and crash rates by exploiting a natural experiment induced by a popular feature of cell phone plans in recent yearsthe discontinuity in marginal pricing at 9 pm on weekdays when plans transition from peak to off-peak pricing. We first document a jump in call volume of about 20-30% at peak to off-peak switching times for two large samples of callers from 2000-2001 and 2005. Using a double difference estimator which uses the era prior to price switching as a control (as well as weekends as a second control), we find no evidence for a rise in crashes after 9 pm on weekdays from 2002-2005. The 95% CI of the estimates rules out any increase in all crashes larger than .9% and any increase larger than 2.4% for fatal crashes. These estimates are at odds with the crash risks implied by the existing research. We confirm our results with three additional empirical approacheswe compare trends in cell phone ownership and crashes across areas of contiguous economic activity over time, investigate whether differences in urban versus rural crash rates mirror identified gaps in urban-rural cellular ownership, and finally estimate the impact of legislation banning driver cell phone use on crash rates. None of the additional analyses produces evidence for a positive link between cellular use and vehicle crashes.

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[…] unknown wrote an interesting post today onHere’s a quick excerptIntuitively I find that using a hand held in a car is distracting at least when Im dialling. Its all in the paper from the looks of it… […]

Gummo Trotsky
14 years ago

It should be noted, however, that our result is not inconsistent with the claim that cell phones are a source of attentional distraction. One possible explanation [for the result] is that drivers compensate for the dangers of cell phone use by driving more carefully. This argument is similar to one articulated by Peltzman in his consideration of the effects of seat belt use (1975).

Similarly, drunks compensate for the dangers of driving under the influence by driving more carefully – but they still manage to have more “accidents” than sober people.

Enough already – is this another one of those research papers that ended up on an institute web-site after it got knocked back by the academic journals?

Gummo Trotsky
14 years ago

Well first up, Nick, there’s no such animal as a “natural experiment”. In this case, although mobile phone sales went up, and mobile phone usage went up, a lot of other variables were left uncontrolled (and don’t seem to have been examined, but I’m only four pages in).

Let’s posit an alternative “experiment” – run a statistical study on car crash rates, correlating them with discount wine sales offers. By the sort of reasoning the paper’s authors applied to mobile phones, we’d expect that when stores are flogging booze cheap, there should be an increase in such accidents, non?

James Farrell
James Farrell
14 years ago

I didn’t go past the abstract, but on that basis the result is completely unsurprising. The rise in calls in the study period is attributed explicitly to the price change. But in the category of calls people make from cars, i.e. urgent ones, the demand is sure to be price inelastic. This is so obvious, however, that I’m sure the study must have addressed it somehow.

Patrick
Patrick
14 years ago

Obvious uncontrollable explanation no 1: cars getting safer at a similar rate to mobiles proliferating.

Non-obvious uncontrollable explanation no 1: talking to someone on a phone reduces one’s inclination and susceptibility to angry responses to other drivers. Maybe as an admitted user NG can comment on that.