Six years ago, when I asked an epidemiologist about a report that a smoking ban in Helena, Mont., had cut heart attacks by 40 percent within six months, he thought the idea was so ridiculous that no one would take it seriously. He was wrong.
Since then, 10 other studies have attributed substantial short-term reductions in heart attacks to smoking bans, and last week an Institute of Medicine (IOM) committee endorsed their findings. But a closer look at the IOM report, which was commissioned by the U.S. Centers for Disease Control and Prevention, suggests its conclusions are based on a desire to promote smoking bans rather than a dispassionate examination of the evidence.
Thousands of jurisdictions around the world restrict smoking. Some of them are bound to see significant drops in heart attacks purely by chance, while others will see no real change or significant increases. Focusing on the first group proves nothing unless it is noticeably bigger than the other two groups.
The largest study of this issue, which used nationwide data instead of looking at cherry-picked communities, concluded that smoking bans in the U.S. "are not associated with statistically significant short-term declines in mortality or hospital admissions for myocardial infarction." It also found that "large short-term increases in myocardial infarction incidence following a workplace ban are as common as the large decreases reported in the published literature."
That study, published by the National Bureau of Economic Research (NBER) in March, suggests that publication bias -- the tendency to report positive findings and ignore negative ones -- explains the "consistent" results highlighted by the IOM committee. But even though the panelists say they tried to compensate for publication bias by looking for relevant data that did not appear in medical journals, they ignored the NBER paper, along with analyses that found no declines in heart attacks following smoking bans in California, Florida, New York, Oregon, England, Wales and Scotland.
If smoking bans reduce heart attacks, the effect could be due to declines in smoking, declines in secondhand smoke exposure or both. The IOM report settles on that last explanation, quite a leap given that "only two of the studies distinguished between reductions in heart attacks suffered by smokers versus nonsmokers."