The subtitle asserting "causality" is offensive. It is alleged that smoking bans in bars have "caused" more road accidents because people are forced to drive longer distances to find those bars that still allow smoking.
To assert causality so starkly for an undesigned observational study is unprofessional. I doubt that the authors of the study they cited even went so far. At best, they probably found a correlation.
Another problem is the practical significance of the finding. There is a 13% increase in fatal accident rate in a "typical county containing 680,000 people". There are two problems with this statement:
- When I check the Census data, there are only about 85 counties in the entire U.S. with at least 680,000 people. What do they mean by "typical"?
- 13% is said to be an increment of 2.5 fatal accidents, presumably per year. The crane accident in Manhattan a few weeks ago killed at least five people. I just don't believe that one can prove definitively that such a tiny difference is not due to chance so even the correlation, let alone the causality, is suspect.
It appears that the paper is locked up in pre-publication. If you have seen it, let us know if the authors actually asserted causality.
Reference: "Unlucky Strikes", The Economist, April 3 2008.