Cell phone use increases the risk of traffic accidents right?  But how do we prove that?  By showing that a large fraction of accidents involve people talking on cell phones?  Not enough.  A huge fraction of accidents involve people wearing shoes too.

I thought about this for a while and short of a careful randomized experiment it seems hard to get a handle on this using field data.  I poked around a bit and I didn’t find much that looked very convincing.  To give you an example of the standards of research on this topic, one study I found actually contains the following line:

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).

(Think about that for a second.)

Here’s something we could try.  Compare the time trend of accident rates for the overall population of drivers with the same trend restricted to deaf drivers. We would want a time period that begins before the widespread use of mobile phones and continues until today.  Presumably the deaf do not talk on cell phones. So if cell phone use contributed to an increase in traffic risk we would see that in the general population but not among the deaf.

On the other hand, the deaf can use text messaging.  Since there was a period of time when cell phones were in widespread use but text messaging was not, then this gives us an additional test.  If text messaging causes accidents, then this is a bump we should see in both samples.

Anyone know if the data are available?  I am serious.