A study recently reported in the journal Circulation finds that the hospitalization rate for acute myocardial infarction among Medicare patients fell by about 6 percent a year between 2002 and 2007. This general trend— which the researchers attribute to factors such as improved medication, better surgical treatment, and a decline in smoking—is one reason it's not safe to assume that reductions in heart attack rates immediately following smoking bans are caused by newly smoke-free air in businesses bound by the laws. Michael Siegel notes that a 2007 study of New York patients "found an 8% decline in heart attacks in the year following the statewide smoking ban," a drop the researchers attributed to the law. Likewise, a 2009 meta-analysis "showed an 8% decline in heart attacks associated with smoking bans in 11 published studies." These results do not look very impressive in light of the pre-existing national trend.
Last year an Institute of Medicine report endorsed the idea that smoking bans have an immediately noticeable impact on heart attack rates. Yet the report's authors declined to estimate the magnitude of the effect, citing the limitations of the existing research. "If the IOM committee was unable to quantify the magnitude of the effect of smoking bans on heart attacks," Siegel asks, "then how does the committee know that the decline was significantly greater than 6%?"
It's true that some jurisdictions have seen drops substantially bigger than that after implementing smoking bans. These tend to be small cities with small samples and volatile admission numbers, such as Helena, Montana, and Pueblo, Colorado. Since hundreds of jurisdictions have smoking bans, there are bound to be some outliers. It is reckless to read data from places like Helena and Pueblo as evidence of an effect unless there is some indication that they are representative. The only nationwide study (PDF) to consider that question—a study that the IOM panelists overlooked in their eagerness to prove the benefits of smoking bans—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."