Why Do Smoking Bans Prevent Heart Attacks Only in Small Towns?

A study in Preventive Medicine finds that a smoking ban in Bowling Green, Ohio, was followed by a 47 percent drop in hospital admissions for coronary heart disease. According to the researchers, "The findings of this study suggest that clean indoor air ordinances lead to a reduction in hospital admissions for coronary heart disease, thus reducing health care costs."

Isn't it funny that jaw-dropping results like these seem to happen only in small towns with small, highly variable numbers of heart disease admissions? Why is it that smoking bans are so much more effective in places like Helena, Montana; Pueblo, Colorado; and Bowling Green, Ohio, than they are in places like New York, Boston, Los Angeles, San Francisco, and Florida, where much larger samples should make dramatic reductions in hospital admissions easy to see?

A look at the raw hospital-admission numbers for Bowling Green, as reported by Michael Siegel, may help resolve this mystery:

1999: 35
2000: 24
2001: 24
2002: 36
2003: 22
2004: 26

Although the smoking ban took effect in March 2002, Siegel notes, the researchers treat that year's admissions as if they all occurred before the ban, which conveniently helps magnify the apparent post-ban drop, since 2002 had an unusually high number of admissions. They also take the number for the first half of 2005 and simply double it to estimate the number for the full year—a maneuver that ignores seasonal variations in admissions but also helps make the post-ban drop seem bigger. Leaving both of those problems aside, how can we reasonably conclude anything about the cause of a post-ban drop in admissions when changes of comparable magnitude occurred in earlier years, for no apparent reason? As I've said before, it's inevitable that heart attacks, purely by chance, will fall substantially in some of the hundreds of jurisdictions subject to smoking bans. That does not mean the smoking bans prevented heart attacks.

In this case, the idea that the smoking ban cut heart attacks in half within three years is especially implausible, since the ban did not apply to all businesses, exempting stand-alone bars and separate bar areas of restaurants. It seems unlikely this law had a dramatic impact on smoking rates or secondhand smoke exposure, and the researchers present no evidence that it did. Given commonly cited estimates of smoking's contribution to heart disease, the ban could not have produced a drop in hospital admissions of this magnitude even if everyone in the whole town stopped smoking.